I use an old Dell Latitude D610 for Windows 7 testing. I still want the Aero interface and the Dell Support web site doesn't have any Windows 7 drivers, let alone Windows Vista drivers.
After some Google'ing and trial and error I have been able to get the Aero interface running in Windows 7 on my D610.
The Dell package that will install the proper driver is R153383.EXE. The package installs the ATI MOBILITY RADEON X300 driver (as displayed in the Device Manager). It shows version 8.360.0.0 and is dated 3/14/2007
I'd host the full file here but it's 59MB and that's a little large. Just Google for that filename or hit http://support.dell.com/ and search for it there.
Enjoy your new Aero interface.