Known issue with AMD dual core CPU's. Installation of the dual-core optimizer from AMD will noramlly fix it for Windows XP.
The samr problem exists for Vista users and AMD dual-core CPU's. However, AMD has not released the patch for Vista yet.
So to fix it for Vista, you need to right-click on the Aces High II start-up ICON, then select the "Compatibility" tab and set the game to run in "Windows 98/ME" compatibility mode. This effectively forces the game to run on one core, but it solves the problem until AMD gets a fix out.
There is nothing we can do, short of a complete redesign of the game, to fix it. The problem has to do with using high resolution timers in combination with being multi-threaded.