I have the same model computer and it works fine for web browsing and general use. I agree with the others that you definitely need more RAM. If you can add just one 512 MB stick to your existing 128 MB, that would give an acceptable performance. 1024 MB would be a lot better.

Those memory configurators that others mentioned will tell you exactly what you can add.

I also agree you should reinstall Windows. What I do is make a restorable backup of the system after completing a fresh install. I use Acronis for this, but there are other programs too. That way the next time things get bad, you can restore your system complete with drivers and applications.

I have also been using Avast free antivirus lately with good results.

Vaya con Dios amigos!
Butch