well ok you can do a repair installation of windows xp without loosing any files or configurations.

First of all boot off an xp cd and then hit enter to setup windows xp. It will search your hard drive and find you already have a copy of windows xp installed. Then you will be given the option to reinstall windows xp in repair mode.

If it works you will be back in business with all your files and configuration and programs working.

If you have an oem computer (ie bought it retail like compaq, gateway, hp whatever) you need to use an OEM version of windows xp to install it. You should have a sticker on the case with the product key on it.

Note by doing this it will be required to activate but thats not a problem because the key on your computer case WILL work to activate it.