For that money he can do WAY better than an 8600GT. Motherboard is a generic pos. Ram should be DDR2800 (he can afford it). You posted the same link for the case + hd, but get a case from a reputable manufacturer - that one is kind of iffy. Coolermaster, antec, etc. will be fine. Rosewill PSUs suck, they are Newegg's "store brand."
Getting an AMD board is stupid atm what with Intel ahead in the processor market plus Intel just made a huge reduction on prices. Not to mention the fact that AMD owns ATI and you are suggesting a Nvidia card...
Research your builds more before posting. That is a REALLY bad computer for the price. Here is my build
ASSUME NO OS/SHIPPING (tax is null unless you live in cali).
Motherboard:
http://www.newegg.com/Product/Product.aspx?Item=N82E16813135059 (ECS P35, great manuf+board)
Processor: Core 2 Duo E8200 - $163 (not yet available at newegg/tigerdirect
PSU:
http://www.newegg.com/Product/Product.aspx?Item=N82E16817189014 (500W Xclio Stablepower)
Memory:
http://www.newegg.com/Product/Product.aspx?Item=N82E16820208283 (2GB Transcend DDR2800 value)
case:
http://www.newegg.com/Product/Product.aspx?Item=N82E16811147095 (rosewill 120MM single)
GPU:
http://www.newegg.com/Product/Product.aspx?Item=N82E16814134038 (ECS 9600 GT 512MB/256bit)
HDD:
http://www.newegg.com/Product/Product.aspx?Item=N82E16822148262 (Seagate Barracuda 250GB 16MB)
$600 or so, tax is null, shipping maybe ~$50, OS whatever
Then you can tweak from there. A different chipset mobo (perhaps 650/680i, though expensive), 4GB of RAM, 3870 or 8800GTS 512 if you can find it cheap, etc. If you want the OS included in that build, just drop the HDD down to 160GB to shave abit, get a similar quality PSU for cheaper, etc. Plus there are ways of acquiring software that you can't with hardware.
My advantages:
Intel board
Much better GPU
reliable PSU
Better Mobo
faster memory
How do you fancy TF2 all high?
I assume you can just pirate a DVD from your old computer...surely your mom doesn't use that often.