Procedural generation has been brought into the spotlight recently (by Spore, MMOs, etc), and it seems like an interesting/powerful programming technique.
My questio
Procedural content generation is now all written for the GPU, so you'll need to know a shader language. That means GLSL or HLSL. These are languages tied to OpenGL and DirectX respectively.
While my personal preference is for Dx11 / HLSL due to speed, an easier learning curve and Frank D Luna, OpenGL is supported on more platforms.
You should also check out WebGL if you want to jump right into writing shaders without having to spend the (considerable) time it takes to setup an OpenGL / DirectX game engine.
Procedural content starts with noise.
So you'll need to learn about Perlin noise (and its successor Simplex noise).
Shadertoy is a superb reference for learning about shader programming. I would recommend you come to it once you've given shader coding a go yourself, as the code there is not for the mathematically squeamish, but that is how procedural content is done.
Shadertoy was created by a procedural genius, Inigo Quilez, a product of the demo scene who works at Pixar. He has some youtube videos (great example) of live coding sessions and I can also recommend these.