You shouldn't have any problems. I was in the same boat when I was first learning OpenGL. You might not already know all of the math involved, but you should be able to get by on some 3D math tutorials, at least for basic stuff.

You'll need a basic understanding of matrix and vector math, but that can be picked up from articles on this site, and once you get it once and learn how to use them, you won't actually see a lot of the math very often.

You'll also need some basic trig, and I mean basic. Given a line with some length at a certain angle, you should be able to find the x and y components using sin and cos. No fancy identities are needed early on.

As far as which language is easier from a math perspective: Neither. OpenGL and Direct3D both let you interface with the graphics hardware, and although they have different styles of doing that, the math will always be the same.

I suggest checking out some of the vector, matrix, and trig articles you can find here or on google, then diving into some basic OpenGL (nehe.gamedev.net) or DirectX tutorials, assuming you already have programming experience. Anything you come across in the near future you shouldn't have trouble understanding.