Are you getting a new monitor, keyboard, mouse etc? Or just using your old ones? If you are using your old ones the following system is $AUD1211- 456 pounds
Athlon XP 3000+ CPU
Asus A7N8X-X motherboard
512MB DDR400 RAM
Seagate 7200RPM 80GB hard drive
Radeon 9600XT 128 MB VIVO DVI graphics card
AVS300 2 satellite 1 sub speakers
LiteOn 52x32x52 CD-RW
LiteOn 451S DVD+/-RW
1.44MB floppy drive
ATX Midi tower case
2 year labour, 1 year parts warranty
I only did that out of boredom, it's a lot better than what you'll need for C2k4 or homework