Trust me, it just isn't that simple.
If it was, every Game would have inherent Direct3D, OpenGL, Glide, S3 Metal, Mesa support etc.
Translating "on the fly" is also no fully possible, since OpenGL does not have equivalent functions for all Direct3D Calls, same is valid for any other API.
It would lead to a myriad of Workarounds and dirty fixes, that would leave the Engine run slow as crap, visually degraded and in the end, buggy...
Just look at the few attempts to wrap Direct3D to OpenGL calls. They code on this for >1 year now, and new DirectX releases actually are done faster than they can even finish the existing one (I think they're still early Beta for DirectX8 > OpenGL 1.2)
Now, there's DirectX9.0b and OpenGL 1.3/1.4 and upcoming 2.0
Believe me, for 2000$ you could take a leading 3D Engine Team "out for dinner", but they sure won't port something for you.
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PS.
This is way Off-Topic now, so you could open a separate Thread for it all on its own