VFP 6 via ODBC and data integrity questions

Good day all, I have just began work on a project to let users subscribe to a service and place orders into a database that is VFP 6 based. Using PHP4, I am able to interface with their program (that also uses ODBC locally) in all aspects (INSERT, UPDATE, DELETE, and SELECT). My worries come when inserting a new user/order from the web. The morons who designed the database made the Primary Key as character and NULLable (once only of course), but I have to deal with that. My question is this... How can I know the new user I INSERT will be unique? (the field is character, but counts like a number field) This especially holds true since I have to deal with local users possibly adding at the exact same moment as PHP (ie. a racing issue). Can anyone tell me how to avoid problems? Would odbc_prepare() reserve a new key for me? Thanks. Brian PJC Services P.S. Kudos to all of the developers. This is a great job you guys are doing.