Very interesting topic. I would post a link to a YouTube video, but it seems to be having a paddy right now
.
Anyway, search for "World of Warcraft iPhone" and you'll find some videos of it on an iPhone, and if you can do it on one of
those things then it must be possible on a
reasonable smartphone/PDA. As far as I know, it has only been done by cracking the iPhone, i.e. using it as Apple never intended, but nearly every other smartphone OS is more accommodating.
If you used remote desktop software, such as the built-in software on WM6, then you don't need DirectX or OpenGL. Only problem would be with the screen size and input method. You could probably write an addOn that would help though.