Writing a C extension

ishboo

Hey all,

I am embarking on the dark road of C extensions and had a few questions in regard to how to go about writing one:

Are there any good tutorials/blogs about how to write an extension. I've been looking but coming up empty handed. I'd love to find one that shows how to make a minimal extension on a Mac, if possible.
How can I make a universal binary (e.g. one that will work on Mac and PC)? Is it possible? Any experience doing one?
Has anyone had experience writing a C extension that downloads a file from a website to the local filesystem? If so, how did you go about doing it?

Any direction/tips/links on these issues would be greatly appreciated!

Cheers,
Dana