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Is your motherboard chipset by any chance a 865PE?
Edit: I just checked and your chipset is indeed a 865PE. There is a known issue with those, whereby if you overclock them past a certain level (usually 230 MHz) you get terrible artifacting in 3D. Are you overclocked at all?
Another vote for a new video card. My bro has a mobile Barton at 2400 MHz. He got a 6800 GT first (which I took over), and then a X850XT. Both cards were a significant upgrade over his old 9800 Pro in terms of playable settings. I doubt he would have seen the same gains had he upgraded his...
Temps are ok if you don't overclock. Personally I got the Zalman cooler and I saw a huge difference. But even so your temps are normal, they're what i saw pre-Zalman. DEFINITELY get a bigger power supply.
->I have a BFG 6800 GT running in an Asus P4P800 Deluxe motherboard
->I have recently installed the Intel chipset drivers and got severe flickering and artifacts in Doom 3, but not in Half Life 2 or Battlefield 2
->power's a plenty (TP 2.0 480), temps are low (Zalman cooler), and the...
1) there's a standard trick to get GRUB to boot XP so you should not have messed with the MBR (Google should have turned it up real quick)
2) now that you did I recommend re-intalling Suse (or whatever Linux you were using) and coming back and asking for advice on how to get GRUB to play nice...
Just so the kids don't get confused: disk reading/writing is many orders of magnitude slower than, for instance, memory access, or any other process happening on the time scale of CPU operation. What that means is that going from a 3.0C to a 3500 won't do jack for your disk read/writes. And...