your ram speed is fine... you just might wanna get another 256 or 512mb stick and throw it in. i saw noticeable improvements on Battlefield 1942 when i went from 256 to 768mb.
your video card is fine. but i'm sure you could definitely benefit from a new processor. but being that it's a compaq, that board might only support up to a certain speed... if i were you, i'd try to find out what that is... and get that speed processor.
those 2 are what i'd definitely get. if you think you need better speakers or another harddrive or something, that's up to you. it all depends on what your needs are. but i'm assuming you play games often, in which case more ram and a new processor would put a lot of life into your comp.