How can I find out if Aero has been configured and running in a Windows 7 Enterprise Edition 32-bit virtual machine?
Right now there are only a few hypervisors that support Aero. As far as I know they are Parallels 4, Hyper-V Server, and VMWare Workstation 7. The problem is a WDDM video driver that meets the requirements. Since virtualization abstracts that hardware underneath, you don't get the full horsepower of the video card.
If you click the Start orb and type Aero in the search box, you will see "Find and fix problems with transparency." If you click on this it will tell you what the issue is that is preventing you from running Aero. If it says the video card doesn't support it and you aren't running one of the previously mentioned hypervisors, you are most likely out of luck.
Note that you CAN get Aero on a VM over Remote Desktop if you have the experience settings turned all of the way up and are running Windows 7 on the host machine as well. So you could fire it up in Virtualbox or VMWare Player, minimize it and then RDP into the VM and have an Aero interface. This works because the graphics are rendered by the host computer and not the VM when using RDP.