Some of the standard things to try/look into are listed in Joe Kissel's recent
Mac troubleshooting: How to handle freezes and crashes. Somehow I don't think that applies here, but it won't hurt to have the list at hand and check the most likely possibilities like hardware test, peripherals, RAM.
I assume that nothing was learned from relevant Console logs? Are the same apps involved in the freezes, or running when they occur? Unfortunately, Artie's suggestion may only be useful when AM's window is visible (including any critical processes) when the freeze occurs.
