I need my database form to programmatically go to the next available number when a check box is set to "yes". This next number in sequence should be five digits, with leading zeros. I'm stumped.

Sounds like you are trying to impose a meaning on an autonumber field.....

within most db engines you can't do that. I suppose you could put a constraint to check the autonumber field was in range 1..99999.

you could handle the leading zeros by formatting in your front end / user interface

BTW what forn end are you using, waht data / SQL engien are you using