Loosely based on the first example found here:
http://www.microsoft.com/communities/new...a0c7968fcb7&p=1

Untested. Doesn't seem all that much different from yours either... but it give it a try.
If AddcomputertoGroup("YourDomain","YourComputer","YourGroup")=0
  ? "Success"
else
  ? "Error"
  ? @serror
endif
 

function AddComputerToGroup($Domain,$Computer,$group)
  dim $objGroup,$objComputer,$RC 
  $AddComputerToGroup=1
  $objGroup = GetObject("WinNT://" +  $Domain + "/" + $Group + ",group")
  if @error=0
    $objComputer = GetObject("WinNT://" + $Domain + "/" + $Computer + ",computer")
    if @error=0
      ;Check if computer already a member of the group. 
      if $objGroup.IsMember($objComputer.ADsPath) = Not 1 ;false 
        $RC=$objGroup.Add($objComputer.ADsPath)
        if @error=0
          $AddComputertoGroup=0
        endif
        exit @error
      endif
    else
      exit @error
    endif
  else
    exit @error
  endif
endfunction