Here is a nice and simple way to get a list of Random PCs.
Create a query based on what you want to find, in my example Windows XP.
Then add to the query a condition to find those with a “3” as the last character in the SMSID,
Since the SMSID/GUID is HEX this will give you ~1/16 of all of those PCs.
R.OperatingSystemNameandVersion like “%Workstation 5.1%”
and R.SMSUniqueIdentifier like “%3”