If you can borrow a full install disk from someone else you should be able to use your valid product key to activate the installation.
If not, you should be able to buy a replacement disk from Microsoft (If you bought a retail version of XP) without having to buy another license.
A local computer shop should also be able to do a fresh install for a fee, again using your valid key to validate.
If you bought a retail version of XP:
How to replace lost, broken, or missing Microsoft software or hardwarehttp://support.microsoft.com/default.aspx?...KB;en-us;326246
If it was originally installed on a computer you purchased:
To replace OEM or System Builder software media, contact the OEM where you acquired the software. To determine whether the software is an OEM or System Builder version, follow these steps: 1. Visit the following Microsoft Web site, and then follow the steps: http://support.microsoft.com/default.aspx?...us;oemdirectory
Edited by Enthusiast, 14 January 2006 - 01:38 PM.