Thanks Wolfgang. I suppose you mean that I need the beta version and not the
stable version. Anyhow, I downloaded the beta version and tried to install tikz
with the command Mojca mentioned in his post. Everything seemed to go on fine.
But when I tried to compile the following simple file I get an error. The
following is the information from the terminal window. It says something like
 ! Undefined control sequence
And on help, it says that "The control sequence at the end of the top line
of your error message was never \def'ed." As you can see below, it loaded the
tikz module. I wonder what the problem is.

******************************************************

MtxRun | loading configuration for
/Applications/ConTeXtMinimals/tex/texmf-local/web2c from
/Applications/ConTeXtMinimals/tex/texmf-cache/luatex-cache/context/3fc847143b06f084e10e73c8fbdf4ae2/trees/3beab8509a03fa29e95f93134a943a7f
MtxRun | loading configuration for /Applications/ConTeXtMinimals/tex/texmf
/web2c
from
/Applications/ConTeXtMinimals/tex/texmf-cache/luatex-cache/context/3fc847143b06f084e10e73c8fbdf4ae2/trees/d9ef00871d7b11751a275cffd8a85753
MtxRun | run 1: luatex
--fmt="/Applications/ConTeXtMinimals/tex/texmf-cache/luatex-cache/context/3fc847143b06f084e10e73c8fbdf4ae2/formats/cont-en"
--lua="/Applications/ConTeXtMinimals/tex/texmf-cache/luatex-cache/context/3fc847143b06f084e10e73c8fbdf4ae2/formats/cont-en.lua"
"./trylua.tex"
This is LuaTeX, Version snapshot-0.35.0
(trylua.tex

ConTeXt  ver: 2009.03.17 11:26 MKIV  fmt: 2009.3.17  int: english/english

system         : cont-new loaded
(/Applications/ConTeXtMinimals/tex/texmf-context/tex/context/base/cont-new.tex
systems         : beware: some patches loaded from cont-new.tex
(/Applications/ConTeXtMinimals/tex/texmf-context/tex/context/base/cont-new.mkiv)
(/Applications/ConTeXtMinimals/tex/texmf-context/tex/context/base/cont-mtx.tex))
system         : cont-fil loaded
(/Applications/ConTeXtMinimals/tex/texmf-context/tex/context/base/cont-fil.tex
loading        : Context File Synonyms
)
system         : cont-sys.rme loaded
(/Applications/ConTeXtMinimals/tex/texmf-context/tex/context/user/cont-sys.rme
(/Applications/ConTeXtMinimals/tex/texmf-context/tex/context/base/type-tmf.tex)
(/Applications/ConTeXtMinimals/tex/texmf-context/tex/context/base/type-siz.tex)
(/Applications/ConTeXtMinimals/tex/texmf-context/tex/context/base/type-otf.tex))
system         : trylua.top loaded
(trylua.top)
fonts          : preloading latin modern fonts
bodyfont       : 12pt rm is loaded
specials       : pdftex loaded
language       : language en is active
system         : module tikz loaded
(/Applications/ConTeXtMinimals/tex/texmf-context/tex/context/pgf/frontendlayer/t-tikz.tex
(/Applications/ConTeXtMinimals/tex/texmf-context/tex/context/pgf/basiclayer/t-pgf.tex
(/Applications/ConTeXtMinimals/tex/texmf-context/tex/context/pgf/basiclayer/t-pgfcor.tex
(/Applications/ConTeXtMinimals/tex/texmf-context/tex/context/pgf/systemlayer/t-pgfsys.tex
(/Applications/ConTeXtMinimals/tex/texmf-context/tex/context/pgf/utilities/t-pgfrcs.tex
(/Applications/ConTeXtMinimals/tex/texmf-context/tex/context/pgf/utilities/t-pgfmod.tex)
(/Applications/ConTeXtMinimals/tex/texmf-context/tex/generic/pgf/utilities/pgfutil-common.tex)
(/Applications/ConTeXtMinimals/tex/texmf-context/tex/generic/pgf/utilities/pgfutil-context.def)
(/Applications/ConTeXtMinimals/tex/texmf-context/tex/generic/pgf/utilities/pgfrcs.code.tex))
(/Applications/ConTeXtMinimals/tex/texmf-context/tex/generic/pgf/systemlayer/pgfsys.code.tex
(/Applications/ConTeXtMinimals/tex/texmf-context/tex/generic/pgf/utilities/pgfkeys.code.tex
(/Applications/ConTeXtMinimals/tex/texmf-context/tex/generic/pgf/utilities/pgfkeysfiltered.code.tex))
(/Applications/ConTeXtMinimals/tex/texmf-context/tex/generic/pgf/systemlayer/pgf.cfg)
(/Applications/ConTeXtMinimals/tex/texmf-context/tex/generic/pgf/systemlayer/pgfsys-pdftex.def
(/Applications/ConTeXtMinimals/tex/texmf-context/tex/generic/pgf/systemlayer/pgfsys-common-pdf.def)))
(/Applications/ConTeXtMinimals/tex/texmf-context/tex/generic/pgf/systemlayer/pgfsyssoftpath.code.tex)
(/Applications/ConTeXtMinimals/tex/texmf-context/tex/generic/pgf/systemlayer/pgfsysprotocol.code.tex))
(/Applications/ConTeXtMinimals/tex/texmf-context/tex/generic/pgf/basiclayer/pgfcore.code.tex
(/Applications/ConTeXtMinimals/tex/texmf-context/tex/generic/pgf/math/pgfmath.code.tex
(/Applications/ConTeXtMinimals/tex/texmf-context/tex/generic/pgf/math/pgfmathcalc.code.tex
(/Applications/ConTeXtMinimals/tex/texmf-context/tex/generic/pgf/math/pgfmathutil.code.tex)
(/Applications/ConTeXtMinimals/tex/texmf-context/tex/generic/pgf/math/pgfmathparser.code.tex)
(/Applications/ConTeXtMinimals/tex/texmf-context/tex/generic/pgf/math/pgfmathfunctions.code.tex
(/Applications/ConTeXtMinimals/tex/texmf-context/tex/generic/pgf/math/pgfmathfunctions.basic.code.tex)
(/Applications/ConTeXtMinimals/tex/texmf-context/tex/generic/pgf/math/pgfmathfunctions.trigonometric.code.tex)
(/Applications/ConTeXtMinimals/tex/texmf-context/tex/generic/pgf/math/pgfmathfunctions.random.code.tex)
(/Applications/ConTeXtMinimals/tex/texmf-context/tex/generic/pgf/math/pgfmathfunctions.comparison.code.tex)
(/Applications/ConTeXtMinimals/tex/texmf-context/tex/generic/pgf/math/pgfmathfunctions.base.code.tex)
(/Applications/ConTeXtMinimals/tex/texmf-context/tex/generic/pgf/math/pgfmathfunctions.round.code.tex)
(/Applications/ConTeXtMinimals/tex/texmf-context/tex/generic/pgf/math/pgfmathfunctions.misc.code.tex)))
(/Applications/ConTeXtMinimals/tex/texmf-context/tex/generic/pgf/math/pgfmathfloat.code.tex))
(/Applications/ConTeXtMinimals/tex/texmf-context/tex/generic/pgf/basiclayer/pgfcorepoints.code.tex)
(/Applications/ConTeXtMinimals/tex/texmf-context/tex/generic/pgf/basiclayer/pgfcorepathconstruct.code.tex)
(/Applications/ConTeXtMinimals/tex/texmf-context/tex/generic/pgf/basiclayer/pgfcorepathusage.code.tex)
(/Applications/ConTeXtMinimals/tex/texmf-context/tex/generic/pgf/basiclayer/pgfcorescopes.code.tex)
(/Applications/ConTeXtMinimals/tex/texmf-context/tex/generic/pgf/basiclayer/pgfcoregraphicstate.code.tex)
(/Applications/ConTeXtMinimals/tex/texmf-context/tex/generic/pgf/basiclayer/pgfcoretransformations.code.tex)
(/Applications/ConTeXtMinimals/tex/texmf-context/tex/generic/pgf/basiclayer/pgfcorequick.code.tex)
(/Applications/ConTeXtMinimals/tex/texmf-context/tex/generic/pgf/basiclayer/pgfcoreobjects.code.tex)
(/Applications/ConTeXtMinimals/tex/texmf-context/tex/generic/pgf/basiclayer/pgfcorepathprocessing.code.tex)
(/Applications/ConTeXtMinimals/tex/texmf-context/tex/generic/pgf/basiclayer/pgfcorearrows.code.tex)
(/Applications/ConTeXtMinimals/tex/texmf-context/tex/generic/pgf/basiclayer/pgfcoreshade.code.tex)
(/Applications/ConTeXtMinimals/tex/texmf-context/tex/generic/pgf/basiclayer/pgfcoreimage.code.tex)
(/Applications/ConTeXtMinimals/tex/texmf-context/tex/generic/pgf/basiclayer/pgfcorelayers.code.tex)
(/Applications/ConTeXtMinimals/tex/texmf-context/tex/generic/pgf/basiclayer/pgfcoretransparency.code.tex)
(/Applications/ConTeXtMinimals/tex/texmf-context/tex/generic/pgf/basiclayer/pgfcorepatterns.code.tex)))
(/Applications/ConTeXtMinimals/tex/texmf-context/tex/generic/pgf/modules/pgfmoduleshapes.code.tex
! Undefined control sequence.
\pgfutil@g@addto@macro #1#2->\begingroup \toks@
                                                \expandafter {#1#2}\xdef #1{...
<argument> ...gf@y by -.5\dp \pgfnodeparttextbox }
                                                   \par \anchor {center}{\ce...
\pgfdeclareshape ... \endcsname =\pgfutil@empty #2
                                                   }
l.549 }
      
? h
The control sequence at the end of the top line
of your error message was never \def'ed. If you have
misspelled it (e.g., `\hobx'), type `I' and the correct
spelling (e.g., `I\hbox'). Otherwise just continue,
and I'll forget about whatever was undefined.

?
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