Depends, is it a prebuilt system (ie Compaq, IBM, Dell, etc...) or is it home built.
If it is a home built system, then all you need do is stick the XP CD in the drive, boot the system, and go through the installation again.
If it is a prebuilt system, then you are pretty much stuck with what ever they give you for a recovery CD. The best advice in this situation, is to uninstall everything that came with it, then use the CD that has just the software on it to install those programs that you really want.