If you have the genuine holographed XP Setup CD, then you could attempt a repair install. Link below tells how;
But heed their warnings, and also I would try to copy off all 'important to you' files, like documents,photos, videos and such before attempting it, as the repair install is not 100% guaranteed.
Have you tried the long-winded manual way to improve performance? eg;
1] Reduce Startup files to the bare minimum using XP's MSCONFIG.
2] Ensure the firewall is on and active, and that your anti-virus is up to date and scans frequently.
3] No other malware is allowed.
4] Uninstall all unwanted and unused applications.
5] Use a recognised and benign 'temp file' cleaner like Piriform's free CCleaner to clean all the junk files out.
6] Use Firefox, or any other non-IE based browser, instead of IE.
7] Keep the system up to date with Windows Updates.
Clean out the dust and grunge from inside the case. Not easy with a laptop but Bob's Sticky thread holds some good advice about that.
That's for starters.