Here's the VBScript code that you'll need. I posted this earlier for a similar post. I demonstrate with the HKLM hive, but this can apply to other hives as well.
'begin script
Dim objShell
On error resume next
''''''''''''''
' Registry key
''''''''''''''
strRegLoc = "HKEY_LOCAL_MACHINE\SOFTWARE\<path>"
strKey = "<keyname>" 'key you'll be creating
strValue = "<value>" 'value within new key
''''''''''''''''''''''''
'write new key and value
''''''''''''''''''''''''
Set objShell = CreateObject("WScript.Shell")
objShell.RegWrite strRegLoc & strKey, 1, "REG_SZ"
objShell.RegWrite strRegLoc & strKey,_
strValueLocal, "REG_SZ"
'end script
You'll need to enter your key name and value into the given script.
Then, create a new GPO, remove all administrative templates for faster policy processing. Go to the scripts section under the desired node (user or machine). Add this new logon or startup script. You'll need to place the .vbs file into its respective GPO directory.
Hope This Helps,
Good Luck!