If you would like to have more ram, and a better vga, than i would say 2x512Mb Samsung (400Mhz)
and for vga: geforce 6-7 series with agp
and for the cpu, just overclock it to 3.5-3.6Ghz
:)
edit: or you can get a new cpu too (Intel P4 3.4 Ghz -- it is realy cheap)