Tom Mulcahy is a Software Design Engineer on the Direct2D team. He posted a cool sample on his blog (Zemblanity) that demonstrates how to do interop between Direct2D and Direct3D10. Check it out.

http://blogs.msdn.com/tmulcahy/archive/2008/10/31/rendering-text-in-the-style-of-the-star-wars-opening-credits-using-direct2d-with-direct3d-interop.aspx