Doug,
The subject of exchanging UML models with Rational Rose is one that frequently comes up. Unfortunately, at this time we do not have the ability to do this. XML is a way to do it, as is dealing with Rose model files or its automation interface, but XMI (a derivative of XML that uses the UML meta-model) is the preferred approach and is something that we will be supporting in the not-too-distant future. But first we need to update Visual UML's underlying architecture to better support organizing the model into packages (and views) so that it is compatible with Rose (and other UML tools). That is the focus of Visual UML version 3.0 (under development).
As for .NET, we are about to releasing a minor update to Visual UML that will enable it to function as an add-in to VS.NET and directly interact with projects while operating in the VS.NET IDE. However, initially it will deal only with C# projects (as does Rose.XDE). Support for VB.NET and VJ#.NET is in the pipeline.
Rob