open regedit and find the key
Select this, on the right there's a binary value called Attributes. Rightclick it, 'modify'. Instead of 40 01 00 20 it should read 50 01 00 20 to have a 'rename' option. In XP, you'll also need to edit the dword string called "CallForAttributes" there. Set it to 0x00000000 (0).