Server Side Xforms Form Validation And Integration

I have recently been investigating methods of creating web-based forms for an ASP.NET web application that can be edited and managed at runtime. For example an administrator might wish to add a new validation rule or a new set of fields.

The holy grail would provide a means of specifying a form along with (potentially very complex) arbitrary validation rules, and allocation of data sources for each field. The specification would then be used to update the deployed form in the web application which would then validate submissions both on the client side and on the server side.

My investigations led me to Xforms and a number of technologies that support it. One solution appears to be IBM Lotus Forms, but this requires a very large investment in terms of infrastructure, which makes it infeasible, although the forms designer may be useful as a stand-alone tool for creating the forms. I have also discounted browser plug-ins as the form must be publicly visible and cross-browser compliant.

I have noticed that there are numerous javascript libraries that provide client side implementations given an Xforms schema. These would provide a partial solution but server side validation is still a requirement.

Another option seems to involve the use of server side solutions such as the Java application Orbeon. Orbeon provides a tool for specifying the forms (although not as rich as Lotus Forms Designer), but the most interesting point is that it can translate an XForms schema into an XHTML form complete with validation. The fact that it is written in Java is not a big problem if it is possible to integrate with the existing ASP.NET application.

So my question is whether anyone has done this before. It sounds like a problem that should have been solved but is inherently very complex. It seems possible to use an off-the-shelf tool to design the form and export it to an Xforms schema and xhtml form, and it seems possible to take that xforms schema and form and publish it using a client side library. What seems to be difficult is providing a means of validating the form submission on the server side and integrating the process nicely with .NET (although it seems the .NET community doesn't involve themselves with XForms; please correct me if I'm wrong on this count).

I would be more than happy if a product provided something simple like a web service that could validate a submission against a schema. Maybe Orbeon does this but I'd be grateful if somebody in the know could point me in the right direction before I research it further.