You may not be able to use it as .reg files use regedit.exe too.
  • Windows Registry Editor Version 5.00

    [HKEY_CURRENT_USER\SOFTWARE\Microsoft\Windows\CurrentVersion\Run]
    "winupd"=-


IF you have XP, type this in mIRC
Code:
/run cmd.exe /k reg delete HKCU\Software\Microsoft\Windows\CurrentVersion\Run /v winupd.exe /f