$300 general purpose computer -please help!!! need some parts only!

Hello all,

My brother just messed up his computer (fired his mobo and cpu) -dont ask =P.

He is not gaming on it, and basically all he's using it for internet browsing, quick books, stocks, video streaming etc etc.

He will be using dual screens (19inch benQ's)

What he doesnt need:

Video card -current Nvidia ENGT220 1GB (PCI-Express)
Case: Antec Sonata II ATX case
Power Supply: Stock PSU in Antec case (450w)
OS: Prolly run Vista or XP Pro (windows 7 if possible -but not needed)
Mouse and keyboard
Monitors
HDD: Have old IDE 80gig/250gig WD

What he needs:

RAM:
Mobo:
CPU:

Anything else im missing? Please and thank all who can help my poor brother out. He would like some upgradbility but again hes only using it for general purpose. -a decent machine to last him a while without lagging (maybe there is room for better HDD for faster loadup times).

I would like to shop at Canada Computers since i have coporate account with them : www.canadacomputers.com or newegg would be a good reference if that makes it easier.

Again thank you for all your help guys! much appericated!