I've gotten that bit working and the functionality I require working...
I now need to close the modal popup box - I've tried various combinations of Modal.Close, with and without parameters (this), (this, "OK"), (this, null) but this doesn't close the modal box from within the code-behind file..
1. The source page using UpdatePanel should be no problem (you open the modal using manual JavaScript).
2. There might be a problem with the target page if you want to use the server-side helper to close the modal dialog. The UpdatePanel intercepts PostBacks and the helper may not work properly.
You should be able to close the modal dialog from the server-side using ScriptManager.RegisterStartupScript: