Hammy, I second Tigas post I'm 99% sure that you have PC2100 512meg. If you double it you will see a speed increase but if you want to make a bigger jump get 2 sticks of 512 PC3200 and you'l have to bolt that little monster to the desk.
The vid cards in store bought puters are seldom the full version of the retail products. If you are really doing a lot of video editind and graphics intensive apps the get a bi fast vid card like a MSI Geforce FX 5900, but prepare for sticker shock that board will set you back $450 at newegg.com Vid editing and graphics really need a board that good. There are more out there that are more expensive but then you get into cards that will never see a store bought computer.
If I remember correctly that computer comes with a 15" lcd, no? Probably a real good idea to get a 18 or 19 for graphics. Hey, it's only money, right?
P.S. just saw the identical system with a $400 card and a bunch of high dollar games for sale at another forum for $699 complete incl shipping. Sold of course.