I like what Microsoft's ESB Guidance kit has done to readily enable and "pre-solve" .NET and JAVA interoperability.  I also really like what our partner, JNBridge, has done with their .NET / JMS adatpers for .NET 3.0 and for BizTalk.  As one of our customers who has been looking for a clean .NET / JAVA interoperability option said "this is progress".  And it really is.  The JNBridge solution is based on the .NET Windows Communication Framework and the JNBridge JMS Adapter for .NET enables you to access JMS services from a wide variety of .NET applications.  The product JNBridgePro is a Java and .NET interoperability tool that opens up access to the entire object-oriented API from the other side, in the same process or across a network. JNBridgePro is a "pre-solved" interoperability solution!  It removes the complexity of cross-platform interop, so that developers can generate solutions quickly (in as little as a day instead of weeks) Go to www.jnbridge.com for more information or contact me directly at hectorr@microsoft.com and I can help you get more information.