Version of WKIX32.exe is 4.11.00. Here's the srcipt I tried to test the ComputerInGroup Function (I put the sllep 10 in order to have the time to read errors but it doesn't work) :

Function ComputerInGroup ($group,$domain)
Dim $oGrp
if not $domain
$domain=@domain
endif
$oGrp = GetObject("WinNT://" + $domain + "/" + $Group + ",group" )
if @error
exit 1
endif
if $oGrp.IsMember("WinNT://" + $doamin + "/" + @wksta + "$$" )
$ComputerInGroup=1
else
$ComputerInGroup=0
endif
endfunction

If ComputerInGroup ("PC-CENT-SI")=1
? 'UDF ComputerInGroup works...'
Endif

sleep 10

Am I wrong ? I guess I am...