General :: Shutdown Windows Machine Remotely Without Telnet / Ssh

I have been trying to shutdown a remote XP machine but cannot get it to budge. I did the following on the Windows box:

Ensured no firewall
Started Remote Registry Editing service
Shared a network drive (to enable file sharing?)
Created a user 'shutdown' specifically for shutting down
Added 'shutdown' to Administrators group
Added 'shutdown' to the list of allowed shutdown users in gpedit.msc

Here's what I have tried:

From Windows 7 box:
shutdown -m computer (Access denied message)
psshutdown -m computer (Access denied message)
runas /user:computershutdown "cmd /K shutdown -m computer (access denied)
runas /user:shutdown "cmd /K shutdown -m computer (access denied)

From Linux box:
net rpc shutdown -I computer -U user%password (says shutdown succeeded) rpcclient -I x.x.x.x -c shutdown -U user (gives usage message)