The blue screen would give you an error code.

Yes quite likely. Your card has two main settings, 2D and 3D. If theres a problem in the graphics card which only shows up when under load you'll have errors like that in games. The reason why Windows mentioned drivers for the video card was the clue as to the reason. My suggestion is to return the card and get a new one, if you can get an HD 5770 because its DX11 compatible.

He also only has a 500w PSU.

Even a cheap 500W PSU ought to be able to drive a GST250 no problems. With PSU problems they tend to be either memory errors or HDD errors as they are both run off the 12V rail.

True, but I mean he's also using an i7 920.

Perhaps the GPU is faulty or something, but just saying.

Thats with a Core i7 at 4Ghz. Im sorry but its an unlikely source of problems unless the PSU is a really crappy and cheap noname PSU. Its a good suggestion otherwise though.

Do you happen to see any ".dll" in the blue screen message? I ask because there were times I'd get a blue screen and see NVIDIA.dll which says that it's something with my drivers and rolling them back to a slightly older version fixed.

i couldnt see as the blue screen dissapear in like 2 seconds and all went blac, i have an eroor code now i think..BCCode : 10000050 BCP1 : B2424000 BCP2 : 00000000 BCP3 : BD1C20B0
BCP4 : 00000000 OSVer : 5_1_2600 SP : 3_0 Product : 512_1

A 500W power supply  has to split it's current between 3.3V, 5V and 12V.  A video card using 150W of 12V power could certainly run out of power with a 500v supply, while the rest of the system is fine.  You can't just add up total wattage and declare there is no problem.

If the vid card crashes when drawing it's maximum power, but works fine otherwise that does  point to not enough current on the 12V rails. Or a flaky driver/directx install.

Take the cover off, and read the current rating for each of 3.3V,5V and 12 V.  It's right there on the side of the PS. That tells you the balance of power the PSU can deliver. If the 12V amperage is less than 40A you are in trouble.    Ideally a good 500W PS would have two 12V lines, each about 30A. That way the PCI-E connectors get their own current ,and the rest of the system gets a separate source. A single 12V 40A line is OK .

My antec 380W PS (Silent, in my HTPC) delivers 38A at 3.3V, 35A at 5V and  24A at 12V - ie not nearly  enough current to power a high end video card. (Note the total wattage adds up to way more than 380W for various technical, philosphical and religous reasons).

Adjust windows settings (google it) so the BSOD does NOT auto reboot.  Haven't used Xp in ages, but there is a setting you can set to tell windows not to auto reboot when a BSOD occurs. That way you can write down what is on the screen...so we have some idea what is going on here...

One more thing to check: It could be that your CPU is overheating. Try downloading CoreTemp at http://www.alcpu.com/CoreTemp/ and then running a game in windowed mode (or using something that stresses the CPU) to see how hot your CPU gets. If it goes over 55-60C, then that's probably the culprit.

You may also want to do the same thing with your GPU by running FurMark for a bit and seeing if your GPU temps go above 80C or so. Your GPU may have a defective cooling unit.

If it's the CPU, then try reseating the heatsink and fan. You may also want to try reapplying thermal paste to your heatsink. If it's the GPU, then it'll probably need to be RMA'd.

But yeah, it may also be the power supply. Do you know its brand name and/or model number? I'm assuming from the odd imbalance of parts (weak graphics card + overkill CPU) that you bought a prebuilt, so the PSU probably sucks. If it is a bad PSU from a generic or third-rate brand, then I wouldn't even bother RMAing it; just grab a SeaSonic or something to replace it.