You can use this online memory scanner from Crucial (a reputable, if expensive company) to find compatible memory modules for your particular PC.Crucial Memory Scanner
There are other companies that have online scanners, to. I think all good memory companies manufacturers have a way to identify what models of their memory are compatible with your PC.
Try these companies, too:
Use Google to locate the manufacturers' web sites by using a search phrase such as "G.Skill memory", e.g. (use no quotes). As long as a company says that a particular memory module is compatible with your exact computer model then you should have no problems with it. Sometimes people have problems when mixing the old RAM with the new - be prepared for the possiblility of having to remove the old modules and put all new memory in. This doesn't happen often, but it does happen sometimes.
I forgot to say that memory prices are at an all-time low. You may as well buy a single 1GB (gigabyte ) module for about $50-$75 USD.
Edited by WinCrazy, 27 September 2007 - 12:55 PM.