No, it's all worked out in the end. I am using the proper version for the Mactel. But...
Running the US version of OS X, which doesn't have a non-Unicode greek keyboard layout, and ArchiCAD _still_ not being 100% Unicode, is a recipe for disaster.
To compound things, XGreek.dmg is not available anymore at
www.vodkatini.gr (the site is not up anymore), Hello Mac OS! although giving greek menus for the Finder and apps it doesn't provide a non-Unicode greek keyboard, so if you have greek fonts they just won't be seen in ArchiCAD, until you install XGreek (that is, if you can still find it).
Fortunately I had saved it locally and installed it. Problem solved.
I just wish that ArchiCAD would become 100% Unicode. Don't know if v11 is. I have it but haven't tried it yet. I also wish that Apple would support Greek a little bit better, to cover all bases. Finally, I wish that the guys from vodkatini.gr who had developed XGreek would carry on their work, or else include it in the current Hello Mac OS! product. After all, from what I understand, they are essentially the same team of enthusiasts.
Thanks for the post, archiben.
Alex Zachopoulos
MacBook Pro 17" 2.4GHz, MacOS X 10.5.6, ArchiCAD 11 & 12, WinXP, Vista (well, not really Vista...)