I need to run a bunch of pluggable processes in a windows service on my server and want to create a user interface that allows me to interact with each of the plugins in use
Your best bet is to use .NET remoting over an IPC channel.
While it seems complicated to setup, it is rather easy the second time around.
I suggest you play with a few samples first on exposing remotable objects from one application to another.
I have not used Message queues before, so I can't comment on that.