Maybe not the exact code your looking for, but this code will check which groups/accounts are on the local machine and report them back.

How many DOMAINS do you have as part of your AD? Maybe some other issue of transitive trusts involved even.

All I can say is that we have over 50,000 desktops with multiple Domains around the globe on AD 2000, and so far all of my scripts work just fine with the InGroup call.

 
Code:
Break On
Dim $SO
$SO=SetOption('Explicit','On')
$SO=SetOption('NoVarsInStrings','On')
 
EnumLocalGroups('your domain','system to check')

Function EnumLocalGroups($Domain,$System)
  Dim $Array,$colGroups,$objGroup,$objUser,$Flag
  $Array = "group",""
  $colGroups = GetObject("WinNT://" + $Domain + '/' + $System )
  $colGroups.Filter = $Array
  $System ?
  For Each $objGroup In $colGroups
    $objGroup.Name ?
    For Each $objUser in $objGroup.Members
      CHR(9) + $objUser.Name ?
    Next
  Next
EndFunction