If all you do is surf the net, listen to music and other things not involving modern gaming on your computer, maybe you should consider installing Linux (Ubuntu). My parents' desktop is from 2003. Only has 500MB of ram and it was very sluggish with its Windows XP installation. I Installed Ubuntu for them. It immediately started acting like a new computer for them in that it was no longer bogged down with start-up programs they didn't use.
I have Firefox open, music playing, and I'm running BOINC . Only 320MB are being used.
So if it fits your needs, give it a try to see if it makes more sense to you then upgrading. In case you didn't know, you can download and burn the installation CD, pop in the CD and you can test drive Ubuntu without installing it/deleting windows/changing your windows settings.
