httpwebwitch - 9:52 pm on Nov 6, 2009 (gmt 0)

Send an invoice.

If they pay it*, give them the files for everything finished so far, but don't do anything more. Continue the project only if you are paid in advance for the remainder of the work.

* From what you've said, that's an unlikely scenario.

...then walk away.

Clients like those are insufferable. Sorry for your loss.

and Welcome to WebmasterWorld!