I am trying to set up a continous integration environment that will automatically deploy an application to a development org every time someone on our development team checks in code into our Subversion repository.  Is there a reasonably straitforward way to clean up all previously deployed artifacts (classes, objects, triggers, pages, ....) on a development org instance in an automated fashion using the salesforce ant library?

I have read replies to other posts that recommend creating a new development org instance to get a clean environment.  However, we need something more repeatable and robust.  We need to run this frequently.  Our goal is to have a true agile process with the SF platform.  Can anyone please help?

Thanks,

Tom