Most likely going to have to try and find a second hand 4800 series graphics card. hes really going to strugle!
for £500 for a tower he could scrape something together, but its not going to be great.
unless he looks second hand for some parts as suggested.
This is what I would get:
AMD Athlon II X2 Dual Core 240 ~ £47
http://www.overclockers.co.uk/showproduct.php?prodid=CP-252-AM
Asus M4A78L-M ~ £47
http://www.overclockers.co.uk/showproduct.php?prodid=MB-377-AS&groupid=701&catid=5&subcat=1482
4GB 1066MHZ DDR2 ~ £71
http://www.overclockers.co.uk/showproduct.php?prodid=MY-192-CS&groupid=701&catid=8&subcat=
OCZ StealthXStream 500w ~ £40
http://www.overclockers.co.uk/showproduct.php?prodid=CA-026-OC
Samsung F3 500GB ~ £40
http://www.overclockers.co.uk/showproduct.php?prodid=HD-081-SA
Asus TA-8H3 Midi Tower Case ~ £20
http://www.overclockers.co.uk/showproduct.php?prodid=CA-040-AS&groupid=701&catid=7&subcat=
Sapphire ATI Radeon HD 4670 512MB GDDR3 ~ £56
http://www.overclockers.co.uk/showproduct.php?prodid=GX-184-SP&groupid=701&catid=56&subcat=
ViewSonic VA2013wm ~ £97
http://www.overclockers.co.uk/showproduct.php?prodid=MO-079-VS&groupid=17&catid=948&subcat=
Microsoft Windows 7 Home Premium 64-Bit ~ £82
http://www.overclockers.co.uk/showproduct.php?prodid=SW-127-MS&groupid=33&catid=1555&subcat=