Cannot install (reinstall) XPSP2 Current Load SP1

Error message - during system backup process:
"C:\windows $servicePackUninstall$ reg00698 SP2 could not backup
registry key
HKLM\SOFWARE\WINDOWS\current version\Windows Update". What can I do,
please?
Reg entry for Windows update = REG_SZ value not set

There is no REG entry for Auto Update under theWindows Update. I tried
to create one but the system advised that such a named entry aleady
existed. I cannot find it. I suspect that, wherever it is it has an
incorrect string value and that that could be the reason why I cannot
recieve automatic updates (Automatic Updates Not Available). Can
anybody help, please