You can still get XP, don’t go Vista yet.
What browser are you using? Try clearing the cache and see if that helps any.
Is it browsing the web the only thing that is slow? Noticed anything else going on? Only certain sites that do it?
Another thing to do is this:
Go to start, click on “run.” Type “cmd.” This will open a command prompt. Type “ping google.com” Let it do it’s thing. If it responds 4 times by saying that it could not be reached or failed to respond, try typing ipconfig /release. Then type ipconfig /renew. This will reset your IP address, and hopefully clear up a problem if that is it.
If you can give me more info, I can try to help.
And maybe that is enough for some good karma. 8-)