As far as I know...Aero is not natively supported in windows 8. However, in windows 8.1 RTM, which is due to release sometime at the end of October, Aero is infact re-introduced in the OS. I can't remember if Aero was working in 8.1 Preview or not. I can confirm, personally that it works in the RTM version. RTM = Release to Manufacturers...the retail giants that build PC's...eg, Dell, HP and so on.
Also worth checking that you have the latest graphics drivers installed, as these have been known to cause issues with the aero interface in the past. As bassfisher mentioned though, aero changed significantly in Windows 8 (it's actually not transparent, just kind of a glazed colour). So the fact that your desktop is showing transparency is strange.