As the others mention you have to write something to get a list of machines in the domain and then go about getting the OS

Take a look at MachineInfo

It will take care of NT and W2K. There are problems with XP and it does not do Win9x.

One thing to keep in mind with the registry approach is the fact the OS is defined by a number. (IE 4.0, 5.0, 5.1) but that is easy to work around.

If you want code for a domain machine list and loop, take a look at Domain Disk space check. It's a little script I wrote. You can get an idea from what I did to loop through the machines in the domain.