DirectX 7 vs 9 in C#

I am writting a 2D tiled game system primarily as a learning tool for C#. I am using DxVBLib (direct X 7.0 DLL wrapped for C#). I am having a problem calling the direct X surfaces on a Thread. It works fine if I am not using threads, but nothing works if I invoke the painting functions in a thread (see related post in the "MultiThreading" forum. My question for this group is whether I should use DX9 instead. It seems to me that DX9 is much too complicated for a simple 2D/Tiled game. It seems more appropriate for 3D stuff. Does DX9 support all the DX7 stuff? I can find plenty of examples for simple graphics and sprites in C++ w/DX7, but none for DX9, which is one reason I decided to try DX7. I also have a couple of books on DX7 (such as Computer Game Programming with DirectX7.0) from Wordware Game Developer's Library. Any suggestions? Dave