Irrlicht Engine

If the graphics card supports non-power-of2 then you can use it in opengl.
Check for GL_ARB_texture_non_power_of_two .

To scale - you could always just adjust the texture coords - 200.0f/256.0f

As for dynamic uploading - I'm not sure how to do it in Irrlicht.
In plain OpenGL, after you've created ...

AFAIK, what you're looking for is the node->getRotation().Y

The rotation returned is a vector with each component equal to the rotation in degrees around that axis.

getHorizontalAngle() would be used say if you had a veloctity vector and wanted to work out the angles from that. Or if you wanted ...

yes, XNA is just another framework - just like popcap / torque / SDL / whatever.

It's biggest advantage is being able to compile to XBOX360 from the same source code.