Dude, any DDR RAM will work, it just will run at a speed up to 400mhz. TBH if you have 1gig thats pretty much all you'll need, another gig won't do much in your case. For instance, I always have limited processes running, I keep my multi-tasking to a minimum, and never use this computer for anything hardcore (it's simply too outdated to do anything special) I'm going to add a 512 stick to my board for a total of 768MB. Thats under a gig, and I bet my computer will never 'starve' for RAM. It's a big misconception that people think that more RAM is always better, your system only uses so much. 1gig is enough for an XP system like that, not really running alot at once (I'm asuming, because those processers don't like to be crammed with tasks) Ask for DDR ram, sized 1gigabyte. If by chance the RAM is not picked up by the system just go into the BIOS and manually setup it's speed (If you don't know how to, any computer store will be happy to do it for you)
~Bryan~