I use a few tools, but one of my favs is AD Info.  It is a free tool (with paid options), and can poll AD for computers.  Things you can check for is last login (PCs timestamp as well) or boot time, OS version etc.  I am not good at writing the AD queries, and this does it for you.

 

Tim

 

 

FYI:
Anyone that has a NOD32 anti-virus Remote Administration server set up can produce a list of computers administered by the server.  That list can be exported as a csv file and it can include the operating system retrieved by the anti-virus client software.  The data are available whether the clients are online or not.  This method is not dependent on the computers being part of a domain and it is not dependent on Windows remote administration being enabled on the client.  I used a list from NOD32 Remote Administration to cross reference the list of Windows XP computers that I retrieved from Active Directory (the comparison was done by taking advantage of findstr.exe /v /i /g).

The NOD32 Remote Administration database, similar to Active Directory, retains computer names even after the hardware has been decommissioned, so I had some cleanup to do in that list as well.

-Stefan