hmmm sounds like he wants the first mac that passes his condition. But the condition to me seems a bit repetitive. I'm thinking something like this.

Note - see how i'm using the code tags

Code:

$PMAC=""
$MACz = WMIQuery("MACAddress","Win32_NetworkAdapter",$IP)
For Each $MAC in $MACz
   If Not $PMAC and NOT InStr($MAC,"50:50:54") 
     $PMAC = $MAC
   EndIf
Next
? $PMAC