Adding Memory!

This will be my first time at adding anything to a computer, i want to play on some good games(WoW) but i only have 256mb of memory so it runs like a tired dog, so im going to add 1gb onto my memory but i wanted to know if somone could link me somthing to tell me how to do add the memory, also i wanted to know that if i added a 1gb memory sticky thing(sorry you can tell this is my first time) would the rest of the stuff i've put on there still be there or would i have to download it all again?

Say.. i have CS downloaded at the moment if i added this 1gb would i need to install it again?

Please Answer and Thankyou!

first off as you don't know much about computers are you sure you've got the wright type of memory. and no non of you programs should be removed as long as you don't break your PC while installing the ram . adam0926