My software is based on this model as well; I use a variety of methods ranging from windows messaging, networking, mutexes, file-mapping, consoles and XML.
This kind of interoperation is not easy when using .NET because DBPRO can't access .NET dlls; not easily anyway. Even for me a frequent user of DBPRO and VB.NET, getting it all to work is a pain; handling the events, creating data packets, security etc; it has taken me months to things working properly; and there is still work to be done.
It is only worth getting into if you a going to release a product or you have lots of time on your hands.
If you can put together an efficient UI with images, sprites, BBB GUI or Top GUI; then go for it. Have a search on the forums for UI snippets and plugins.