Hmm PC800? Never had it myself. I'm currently using Kingston DDr2. Depeneds on what your current bus speed of your mother board is. Is it an 800 mhz one? That would mean you can get a better board and will also need the new ram to put in it.
Check out some Alienware computers if you don't want to build one yourself. They are now owned by Dell but you can see from the specifications of them to see what you need for a decent gaming rig. (or you used to be able to before Dell...)
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