I tried installing NeoOffice in the meantime to reproduce the problem, but there was no crash and amule just ran fine. So it does not seem likely that NeoOffice is to blame for your problems.
@Kry
I agree with you, the system wide spell checker *should* not be able to get crashed by an app using it. But given the sequence of events (spell checker crashes the moment amule is started), it looks like this is exactly what happens. Since aMule does not make any explicit use of the spell checker, it seems like the problem could be that wx sends some malformed request to the spell checker, which in turn does not handle that request as gracefully as it should.
@plugues
I just had an idea, could you try starting your Mac in safe-boot mode by holding down shift during startup? That way, no 3rd party extensions and the like would be loaded, and it would be very interesting to see if the spell checker still crashes and aMule refuses to start. Not that this would be a viable long-term workaround, but it might give us a better idea of what is going on.