420 budget for gaming rig please help.

Im planning to build a pc as budget performance as possible im an intel fan but i want to try amd also.

i have my new 19'' syncmaster widescreen but problem is i cant enjoy this monitor cos of my old pc

P4 3.4Ghz
PM8M-V msi
2ghz pc3200 400mhz
x1650 se ( not pro ) that a ***

please share me your opinions choosing pc parts!..

anyway havign a second thoughts just to upgrade my agp gpu

to 4670, 3850, 3650, 4650 AGP's

Budget upgrade?

new Rig?..