Some times Registry is disabled in Xp due to virus or whatever... Here is a way u can re enable it
u must be Admin not a limited user on ur machine for this.


Goto run type gpedit.msc
hit enter
now on left pane select User configuration
then select Administrative templates
then select system
now look on right pane
Double click on Prevent acess to Registry editing tools option
select option Disabled
click OK
thats all Registry will be enabled.