James Senior has a post on his blog “Views on Vista” that details how to build WMI filters for Vista and Server 2007 (Longhorn).

For Vista and Server 2007 essentially you look for OS version >= 6 and for Vista a product type that = 1 and for Server 2007 a product type = 3.  Check out his post below for the exact syntax.

For Vista 

SELECT Version, ProductType

FROM Win32_OperatingSystem

WHERE Version >= '6' AND ProductType = '1'

For Longhorn Server

SELECT Version, ProductType

FROM Win32_OperatingSystem WHERE

Version >= '6' AND ProductType = '3'

I created a quick script to show the results (click for larger image):