I'm always amazed at how many folks ran WinXP on 1GB of RAM. The stuff has been so cheap for several years, it just doesn't make sense. I've been doing IT for about 14 years, and aside from upgrading the Processor (which means another motherboard), Adding RAM is the biggest boost you're going to get. Also, if the computer uses DDR memory, then you need to add the RAM sticks in pairs to get the performance out of them.

Most motherboards have 4 slots. As an example, the link below is for an older DDR set of two 1GB sticks for $69 bucks.

http://www.newegg.com/Product/Product.aspx?Item=N82E16820231047

Remember that XP can only address about 3.5GB total so 4GB is the practical limit in installed memory.

One other thing to consider: If your C: drive is more than half full on XP, then each and every thing you add to it will slow the computer down more. It's a flaw in the operating system.

Just my $.02,

Charles