There will be a DHCP server on your AP, probably just not turned on.
To make things secure, have a shared drive on the desktop pc which everyone has write permission to, you share this drive for customers to copy on their files. If you dnt want them to be able to access the rest of the network, best to isolate the wireless part of the network to its own sub domain. Different IP range etc (can do this all via the AP)
However you will have a bunch of security issues by having an open network, (assuming any customer can walk in and connect to it) even if it is only sharing one network drive. I can think of at least half a dozen things someone can do, to cause havoc, if they find a open wireless network thats easily connected to.