Using Group Policy to push out software to computers with different OSs

Is there a way to selectively push out software, through Active Directory using Group Policy, for computers with different operating systems? An example would be our Windows 2000 Pro machines need Acrobat Reader 6.0 pushed to them, where our Windows XP Pro machines already have Acrobat Reader 7.0 installed on their base image.

Absolutely possible! There are two ways. One way is to create two OUs: one which contains Windows XP machines and the other which contains Windows 2000 machines. Then, simply link the GPOs you want to affect each type of machine.

However, this doesn't help much if both types are mixed together. Say you have an OU called "SalesComputers" with both a mix of Windows XP and Windows 2000. In this case, the best way to achieve your goal is to create two NT-style groups: one containing the Windows 2000 computers and the other containing the Windows XP computers. Then, link the GPO that you want to affect, say, only the Windows XP computers to the SalesComputers OU. Finally, remove the default "Authenticated Users" group and add in just the group containing Windows XP machines.

Likewise perform the same steps for Windows 2000 machines, and you should be golden.