To delete a registry key and its subvalues:
REG DELETE HKLM\Software\TestKey /f
(Available in Microsoft Server Resource Kit - free download - I used the 2003 ResKit - and just put the code in notepad)
Also, there are a lot of other registry functions with this command like: add, copy, save, load, restore, compare... (REG ADD, REG LOAD, etc). And within each function --> there are more switches. Very nice.