Yeah ram is an easy upgrade
I really do suggest buying online, you save a bundle and stores like newegg.com are reliable
If your using DDR SD RAM, get the cheapest PC3200 ram, it doesnt matter if you are using 2700 or 2100 though, 3200 is backwards compatable and just as cheap. Their's no point of getting a stick less than 512 meg as well as a few more dolalrs gets you 512.
Also if you buy 3200 (same price) and a 512 meg stick, if you ever upgrade your PC (you have a dell, stick around here and you will) or buy a new one you can stick it in a new PC most likely as well as the possibility of your ram running in Dual channel, which doubbles memory speed