I've recently upgraded my OS from 10.5 to 10.6.8 Snow Leopard.
I use Mail app and have two accounts; 'work' and 'personal'. If I go the Mail Preferences and make the 'personal' account inactive Mail crashes and I get a warning message saying; 'Mail quit unexpectedly'. If I go to Mail Preferences and make the 'work' account inactive I can not close the Mail Preferences window.
I also installed Rosetta. I understand this only works when needed with legacy Power PC applications, so I presume this isn't causing the problem.