Thank you for your post.
When you mention "the accounting portion", can you be a little more specific? That is, what is the name of your database file? How many tables are in the database file? If it is crashing in a particular layout, is there anything you are doing just prior to the crash? Have you tried to recreate the layout?
Although FileMaker Pro 8.5 was the first version to be certified with Mac OS X 10.5.x (Leopard), I do have FileMaker Pro 7 on my machine with Mac OS X 10.5.8, so I can try to replicate the problem here.