Otherwise you could take a look at the DXUT-Framwork from Microsoft it does just what you want...for example in CustomUi (part of the SDK). Maybe you can get some ideas from them how to solve your problem.

Thanks for the replies, though I think for the sake of simplicity (this is just a simple demo) I'm going to go ahead and just shut off all models when something like Inventory or Bartering is enabled, this gives me a nice flat surface to toss text onto. I think I'll look into DXUT a bit more for the next time around, that CustomUI has some very cool stuff in it.