The only thing, other than a corrupted attachment, that should cause any glitch woudl be fonts (although CS2 should give a warning and substitute default font). If you included an unembedded pic, that could also cause some grief.
First try resending, without any compression like .zip, to make sure the attachment wasn't simply corrupted. There's usually no reason that the mac won't open the AI.
You can also try sending an eps without fonts outlined and see if that works. Tell the recipient what fonts you used. If there's a font problem and no further editing is necessary, try outling the fonts and send either an AI or EPS.
Using OSX 10.3.9 on a G4