Registry Editing has been disabled by your administrator

Many people face this error message when they try to open Registry Editor and they have a malware/spyware installed.

Thanks to http://windowsxp.mvps.org/tweakuirest.htm the following gives the solution for the same:

Removing the DisableRegistryTools restriction

For standalone Windows XP systems, perform the steps below to remove the registry editing restrictions.

Method 1: Using the REG.EXE console tool
1. Click Start, Run and type this command:
REG add HKCU\Software\Microsoft\Windows\CurrentVersion\Policies\System /v DisableRegistryTools /t REG_DWORD /d 0 /f

Please note that the above command is all one line, so please copy the complete command and then run it.

You should be able to launch Tweak UI, as well as the Registry Editor.

Method 2: Using the Group Policy Editor (Windows XP Professional only)
Click Start, Run and type gpedit.msc and press ENTER
Go to the following location:
User Configuration Administrative Templates System
Double-click Disable registry editing tools and set it to Not Configured
Exit the Group Policy Editor

Note: If the setting already reads Not Configured, set it to Enabled, and click Apply. Then revert it back to Not Configured. This ensures that the DisableRegistryTools registry value is removed successfully.

Spanish version of the article is here.