At the risk of being extremely ignorant here, you should be able to edit the form (assuming you have the right permissions) from the mdb file. The "code" that runs the forms, etc. isn't actually compiled in the traditional sense, rather it's interpreted at the time that it's called.
If Access doesn't automatically show you the window that will let you edit the forms, you should be able to get there via the Windows menu. If not, search the online help for "startup form" or something like that.
Sorry for the vague instructions, I'm moving offices, and my pc with Access is in pieces on the floor here.
If I'm wrong, someone please correct me.