Please tell us more about the computer. How old is it? Has it run correctly before? Brand name? Home built? You mentioned the problems happen shortly after installing XP... Which version of XP? SP2? Are you installing XP from the computer Recovery Discs or from an XP disc? Is it a full and legal XP disc from Microsoft?

Did you install all the hardware drivers?

If the XP installation is legal and correct, then the hard drive is my first guess.. The files are becoming corrupted shortly after installing.. Have you done a full Chkdsk to determine if there are bad sectors?

Hope this helps and let us know more.