Hmm, sounds as if you are dealing with a failing or corrupted Hard Drive. You can boot from the Windows XP CD (as you did before) and there should be an option to repair a Windows installation. The repair process will restore all the Windows files (including the one you are missing).
http://www.microsoft.com/windowsxp/u...ps/doug92.mspx

However, after you get back into windows, you should back up all your important files, and run 'chkdsk' on your hard drive.