Sorry ciro, but i like write tex code.
  1. save following code as test.tex
    %%
%% save it as test.tex
%%
\setupcolors[state=start]
\starttext
\dorecurse{660}%
{\startTEXpage[width=3cm,height=2cm]
\vbox to \vsize{\vss
\hbox
to\hsize{\hss\framed[width=2cm,align={middle,lohi},background=color,backgroundcolor=green]{p.\tfd\recurselevel}\hss}\vss}
\stopTEXpage}
\stoptext
  2. create the pdf
    $>texexec --pdf test.tex
  3. Save the following into my-imp.tex
    %%
%% save as my-imp.tex
%%
%% \setuplayout
\starttext
\centerline{%
\externalfigure[test][page=1]
\externalfigure[test][page=3]
\externalfigure[test][page=5]
\externalfigure[test][page=7]
\externalfigure[test][page=9]
\externalfigure[test][page=11]
}
\blank[1cm]
\centerline{%
\externalfigure[test][page=2]
\externalfigure[test][page=4]
\externalfigure[test][page=6]
\externalfigure[test][page=8]
\externalfigure[test][page=10]
\externalfigure[test][page=12]
}
\stoptext
  4. create the pdf
$> texexec --pdf my-imp
  5. the first page of my-imp.pdf now has  12 pages from test.pdf;
Now, if you have yourfile.pdf you can replace
\externalfigure[test][page=8]
with
\externalfigure[yourfile][page=8] etc.


\externalfigure has parameters page,width,height, etc...;
you can use it to scale to appropriate dimensions (they depends by size of paper);search on wiki for externalfigure


Usually i make simple scripts that create my-imp.tex with correct pagenumber (ie the pagenumber that i want to select); also i use \clip (search on wiki) to correct some page and pdfinfo to have some informations on pdf files.

But hans also replay with a quick and clean solution.....



luigi