Backup your files
Keep current backups of all personal and system files. A backup can restore lost data in the event your system's security is compromised or your critical files become corrupt.
What system files to backup?
Daily backups of your registry files are recommended. In addition, always create a backup before installing any new program or making any changes to your system settings.
Since system files in Windows XP cannot be simply copied while they are in use, XP users should use System Restore to create restore points. (A shortcut is placed by default under System Tools in the Start Menu, or you can find it at %SystemRoot%System32restorerstrui.exe.)