Phil,
Here is another method similar to Kent's code.
You could do this one by one, but the best thing to do is probably read a file with the names of the computers you want to perform this task on, or a similar method.
I'd first have it ping and if successful run this code but supplying the computer name of the read in one each time.
This code allows you to add either Accounts or Groups.
Code:
Dim $SO,$AddAdmin
$SO=SetOption('Explicit','On')
$SO=SetOption('NoVarsInStrings','On')
$AddAdmin = AddToLocalAdmin('TestComputer','Administrators','YourDomain','ITSupport')
Function AddToLocalAdmin($Computer,$GroupToAddTo,$Domain,optional $GroupToAdd,optional $AccountToAdd)
Dim $Group,$User,$Admin,$Err
$Group = GetObject('WinNT://' + $Computer + '/' + $GroupToAddTo + ',group')
If $GroupToAdd<>""
$User = GetObject('WinNT://' + $Domain + '/' + $GroupToAdd + ',group')
EndIf
If $AccountToAdd<>""
$User = GetObject('WinNT://' + $Domain + '/' + $AccountToAdd + ',user')
EndIf
$Group.Add($User.ADsPath)
$Err = @ERROR
$AddToLocalAdmin=$Err
EndFunction
Function fnCOMErr($lErr)
If $lErr<0 $lErr=VAL("&"+Right(DecToHex($lErr),4)) EndIf
Exit $lErr
Endfunction