Help me upgrade plz

[Makaman]

I wanna upgrade my bros PC need to get a 512 stick of ram and a 3d card...I know what kinda 3d card to get but dont know ram.I know its DDR ram But i know there is like 300 400 mhz ram or sometihng like that..How can I tell what to get?
The pc is a HP pentium 4 2.6 ghz.
Thanks!

 

[jack22]

Download cpu-z and click on the memory tab.