Is it possible to divert some of my cpu RAM to my video card? I have plenty of ram to spare on my machine, 2.5 gigs, and wonder if I can transfer some of it the graphic card so I can play a game like Doom3.
No, you can't physically transfer your RAM from your machine to your video card. Nevertheless, your video card will still automatically use your system RAM the moment it runs low, thanks to AGP.
So even if your video card has only 64 MB RAM, it can access more from the system if it needs it.
So can a card with 128 mb of ram (Radeon 9600) play a game like Doom3 that requires 512mb ram for full texture features on a computer with 2.5 gigs of ram? Or no? I am running a G5 dual 2.0 machine with 2.5 gigs of ram.
Well there is also an "Uber graphics" mode that is tailored for video cards with 512 MB video RAM. But it's optional so you shouldn't worry about that.
Your system will be able to play Doom3. How well and how pretty... are variable.