I think a lot has to do with hardware compatibility. I was running the 32 bit version with as many of the drivers updated to the 7 version as are available, but still ran into one problem after another. Since the machine I was running it on is archaic by PC standards (Athlon XP 2800, nVidia 7800 AGP card (the horror!), and a Soundblaster Live! Value card) I can only attribute others' success at installing and running some of the very same games I cannot run as being hardware related.
For example, the Sounblaster Live! cards are not supported by Windows 7, but the were by WIndows XP. Games that required a soundcard be installed ran fine on XP, but not 7 because it does not recognize the card is there. Other issues I believe are related to the fact that my graphic are being piped through an AGP card. Vista doesn't like AGP cards much, and 7 not at all, but it does recognize it and allow it to function, albeit at a performance hit.