UP-DATE PROCESSOR

it is a matter of socket..your processor is normal AMD XP 2500 ++ which fit in the socket of the board..that socket is quite'old'///It is called socket A.in this socket you cant put a new athlon 64 proccesor...it will never fit..the 64 athlon has slots like 754 or 939.....and now 940...well...for the processor you need to change the board...and for the video board...you should change it too..the pcie is a special slot...the pcie express video card will never fit in the agp slot:)
oh...the performance is much higher...you really should do this upgrade..
here is  areview of your chipset
http://www.amdboard.com/qdi_k7s746fx.html