Lookup and/or create new record from same box?

Here's what i'm trying to achieve.

I want people to be able to look up a client by their unique ID number. I
know this is easily achievable through a lookup box. Not a big deal, i know.
What i'd really like to do, is to be able to type in the said number and
have it search the table for that record and go to it, if it exists. If it
doesn't exist, i'd like it to tell the user that the record doesn't exist,
but prompt them with a yes/no box (or something) to create a record with
that ID if they like. Then, pass that ID on to the new record.

Is this even possible? Or is there a better/simpler way that i'm not even
thinking of?

Thanks
Mike