If your system failes to start due to an error related to missing HAL.DLL, invalid Boot.ini
or any other critical system boot files you can repair this by using the XP installation CD.
Simply boot from your XP Setup CD and enter the Recovery Console.
Then run "attrib -H -R -S" on the
C:\Boot.ini file and delete it. Run "Bootcfg /Rebuild" and then Fixboot.