If you have Windows XP Professional and access to an administrative user account, you could change the registry editor options in the Group Policy Editor.

1. Click Start, Run
2. Type GPEDIT.MSC and Press Enter
3. Go to-->* User Configuration-->* Administrative Templates-->* System

4. In the Settings Window, find the option for "Prevent Access to Registry Editing Tools" and double-click on it to change.
5. Select Disabled or Not Configured and choose OK
6. Close the Group Policy Editor and restart your computer
7. Try opening REGEDIT again