Other ways to reach the application data path is to enter %appdata% into the address field of your windows explorer. Or is that does not work: %userprofile%\Local Settings\Application Data
I asked this question a while ago (not that I use Vista, but a player in a game I was organising did), and this was a useful response I got (from Ballbarian):
If you go to one of your dominions saved games folders, such as
C:\Program Files\dominions3\savedgames\CasualPBEM
there is link in the explorer window called compatibility files. If you click on it, it will bring you to where the actual files are stored. (the first link I gave)
The easy way I hear is to not install dominions into the program files folder.