As long as you run the default configuration under Vista, you will suffer performance problems. Theoretically, SP! for Vista is supposed to help address this. Whether or not it does, remains to be seen.
The big issues with dual core AMD CPU's and Vista is the bug that plagued XP until AMD and Microsoft released patches to fix it. For Vista, there is no patch available. As Aces High II hits the bug in the AMD dual-core CPU, you are relagated to running the game in "Windows 98/ME" compatibility mode.
I have not heard if this will be addressed in SP1 for Vista.