As far as I am aware the only version of Maya that has Vista Support is 2008. Neither 8 or 8.5 is designed to support the Vista Architecture...
If you both have Vista and 8.5, then try:
Updated Drivers from your VGA Cards Website
Do not use custom drivers sets (like omega)
Downgrade to XP
Go get Maya 2008.
Chris (formerly R@nSiD)
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