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Probably running it in Windows. I think you can get the ATI X1900 and the 8800 series to work side by side in a mac... from what I read.

No, you have to remove the X1900 XT and put the 8800 in when you want to game with it. If you want to go back to OS X later, you have to remove the 8800 and put the X1900 XT back in. It's a pain in the ass, but to some it's worth it.
 
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