Seems we never posted the conclusion about this problem: XeTeX simply doesn't work with the old Mac Type 1 Postscript fonts on Mac OS X (Leopard or before). The reason is that these old fonts store their data in the resource fork, which Unix utilities like XeTeX don't see. Only TrueType or OpenType fonts will be recognised and loaded correctly. PCs don't have the data fork so old Type 1 Postscript fonts for PCs (with .pfb extension) seem to work. Just copying these to the Mac is no solution, however, because Mac OS X does not support PC-style Type 1 fonts (only the Mac ones with the data in the resource fork), and therefore XeTeX will not find these fonts. Therefore the preferred solution is to use fonts of TrueType or OpenType varieties. For those with access to a font conversion program like fondu (?) fontforge (?) or fontlab (?) it may be possible to convert the old Type 1 font to TrueType or OpenType, reinstall it and have XeTeX work with it in that way.