If the computer is still running slow, you should make sure it isn't an overheating problem.
Download and install
Speed Fan.
Run it and find out what the
temperatures are.
If any of them are at/above
60*C when your computer is
Idle, I would have a look
HERE for cleaning tips.
Also make sure you have enough cooling in your computer. If it is possible, get a large external fan (like a Tower Fan) and face it at your computer and see if the problem still persists.
As for
RAM (Random Access Memory), if you
Right Click My Computer and go to
Properties, you will be able to see the basic System Specs.
We recommend you have
AT LEAST 512mb RAM for Windows XP,
1gb recommended.
As for Windows Vista, depending on which Vista Product,
2+gb is recommended.
It is recommended you have at least:
512mb RAM for Windows XP
1GB for Windows Vista
2GB for Windows Seven
2GB for Windows 8