Here is the best deal as far as price and a good brand goes.
Patriot 2 x 1gb. 2GB Total Buy 2 of these kits so it will equal 4gb which is the max your computer can take.
If you have a 32bit Operating System, which you probably do it will only recognize about 3.5GB. But, with your computer you have to install matching pairs so you have no option to just install 3 1gb and a 512mb. You have to go all the way to 4gb to max it out.
If you only want to have 2GB then just buy one of those kits. It will be 2 sticks of 1GB.
Here is a list of all the RAM that will work with your system.
CLICK HERENames you should trust and that are good are Patriot, OCZ, and G. Skill to name a few.
Here is what I would say is the absolute best for your computer.
Corsair Dominator
You can buy just one of these kits (2 sticks of 1GB) or you can buy 2 of the kits to equal a total of 4GB which is the best and good for Gaming.
Do you need help on the install of the RAM? I can provide manuals, instructions etc if you wish.
Let me know what you think. If money wasn't an issue and you want the best, get the Corsair Dominator. The second pick is the Patriot brand I recommended.