peterdaly - 5:03 pm on Aug 15, 2008 (gmt 0)

Ask that he pay what he owes, and the the arrangement now needs to be a payment up front for any additional work.

That being said, you can split up future work into smaller blocks (milestones?) so he doesn't have to pay for a large project up front, but you are still working against already paid hours.

If he has problems with that, it's time to walk.