What you are seeing is called a kernel panic. And there
should be no way for an application to cause that. Basically, it indicates a bug in the kernel (or some kernel-level driver). Now it is possible that such bugs in the kernel are particularly sensitive to the behavior of certain applications but not others, but that doesn't mean it's the application's fault.
In the case of aMule, there are no reports of kernel panics from other users.
The most likely cause of kernel panics in Mac OS X is actually bad RAM. Check out
this link for a lengthy discussion of the topic. If you added third-party RAM, try removing it to see if the kernel panics go away. If you bought from a reputable source, they should replace it free of charge.
There are other possible causes (hardware issues, misbehaving drivers, etc.), but aMule isn't one of them. Make sure to report the kernel panics to Apple (the OS should automatically offer to do this) and maybe bring the system in to an Apple Store to be checked out.