Ask if hes willing to reuse (If he had a previous Computer) his old mouse, keyboard, speakers and moniter.
Because it would really help save money so it can be then used to buy everything else.
If not, itll be a tighter squezze but its still doable.
I dunnue prices off the top of my head but Ill do my best with a no link build.
Fortron (450 Watt) / or/ Hiper (530 or 580 Watt)
Gigabyte 7800GT (Or 8800GT if enough Money)
Seagate 250 (Or 320GB or less, w/e) GB 16 MB Cache SATA
Some sound card (A cheap but still good one is Audigy 2 ZS
OCZ 2 GB DDR2 800 (2 X 1 GB)
Some Case w/Fans
Meh, something Like that.. Put that together with links then we can see how much you have to play with.