The registration of DD filter under Vista has been explained several times on this forum but I will repeat the trick once again :
You have to run the DDReg.bat file after deactivating the UAC feature of Vista. To do so, one way is to do :
1/ Run MSCONFIG (from the command prompt or from the Control Pannel / Administrative Tools)
2/ Click on Tools
3/ Search for the line "Disable UAC" and click on it
4/ Reboot
5/ Run DDReg.bat
6/ Enable UAC the same way you disabled it (search for the line "Enable UAC")
Another way to disable/enable UAC... ( with screen shots

)

Click on the link "Turn User Account Control on/off"

Validate this message by clicking on "Continue"

Uncheck box

Reboot PC
At next start you will probably notice this advice :
Et voilÃ
... I think you should be able to find the way to re-enable UAC on your own
Concerning the Aero interface, DD is not fully compatible so you have to deactivate it before running DD. You can totally deactivate it or simply modify the DD's shortcut in order to deactivate it at DD start and reactivate it at DD stop.
To do so : Right-Click on DD's shortcut - Select "Properties" - Click on "Compatibility" - Check the "Disable Desktop Composition" box