You being an audio guy, I would learn to program first. I think the most important ability for a designer to have, is to being able to implement ideas quickly. To me a design is just a hypothesis, which will either be proven, or disproven by a prototype. If you can't program, you will never get feedback on whether or not what you're designing is actually fun, and your design skills will never progress.

A hard truth, is that 80% of the ideas a designer comes up with, are going to be bad. I read a book 10 years ago, where Sid Meier stated that he had roughly 40 prototypes that he had written, collecting dust on his hard disk. That is what makes him a great designer, he has enough sense to test out his ideas, and only go with the ideas that actually turn out to be fun.

I would skip writing a really long design document, and instead put that energy into learning to program, or learning the scripting language of a game in a genre that you are passionate about. Then I would start with simple designs, implementing them, and seeing how they pan out.

Hope that helps.

It depends strongly on how much interest you have in programming and what sort of games you wish to program. The best thing to learn would, in my opinion, be C++. It offers great power and flexibility, but some find it rather challenging to learn.

Hmm, on a PPC Mac your options are somewhat limited. There's a version of Blitz Basic for the Mac, which will enable you to get something on the screen prety quickly. As an audio guy, you might want to try one of the audio languages, like ChucK, http://chuck.cs.princeton.edu/ , which might be more interesting to you.

I would try to get an Intel PC of some sort, it will open up a lot of options in terms of the scripting languages you can learn.

Hope that helps.