I think the patch from MS is more an OS type patch than a game specific patch... so should work for all games i reckon.

Cant say if going to Vista will solve the problem but Vista was designed to make use of dual core processors so who knows. Cant you borrow a Vista disk somewhere and do a trial install first before buying it? You can install Vista without a key so if you can borrow someones disc first to test it could save you money. You can use it for 30 days if i remember correctly.

I have a dual boot system with both XP SP2 and Vista on and I cant really see a difference in viewport performance between the 2 OS's. Then again.. I am just starting out with Maya so havent loaded any complicated scenes or anything.

I almost would have thought that your problems would be more graphics card related than cpu related... drawing the viewports seems more of a graphics thing than a processing task.... very strange problem indeed.