well ram will make it slightly faster, but it wont be like switching to sdram, (adding 512 is such a minimal difference, but the price is ok so go for it) there are always exceptions liek speeds but you shoudl eb able to get them working
if you want to make sure it wil fit, turn off your computer take one of your sticks out and compare it to the pic on ebay, and dont forget what slot it was in on your mobo
, its just two little latches on top and bottom then they come right out
i recommend a full reinstall of windows xp if you can do that, and it doesnt aggravate you to reinstall all your games and apps, this will give you much better preformance, unless over the years you have been very good with anti spyware and firewall protection.
i can give you a list of programs to get when you reinstall(virus stuff, computer monitors)