As I have no idea how to reach the original developer, I don't even know who it is, and there is no progress in development anymore since a long time, I fired up my hex editor and patched the internal detect string "REGEDIT4" at offset 0x00009278-0x0000927F with zeros.
The effect is that now you can open all reg files in TC regardless of file header if the reg file is DOS text, so either convert the .reg-files before entering or directly create them using REGEDIT-Export-W9X/NT Regfiletype.
@all:
Of course I take no responsibility for any damage on your system. Life is a risk so always make backups before using.

@author of plugin:
Forgive me but I think it's at least a nice workaround till you continue working on that nice thing. Under 2000/XP it's really not very comfortable to use otherwise...
Scroll down on the site and click button "Free":
http://rapidshare.de/files/16681532/WCReg_1_4_patched.zip.html
Icfu