I know that sounds like an older idea.
I don't want replies of "Why would you want to do THAT?"
My answer to that is: So I can know how!
What languages do I need to know, and what do I do in general?
I want to start small... Say, a printer?
I know I'll probably need some knowledge of micro-controllers.

Not sure why you need a poll for that

Anyway Google provides a lot of answers to the question how-to write a driver.

This one looks interesting for instance.

Sorry about the poll... Just playing with the site :P
And thanks.

There is a really thorough book called "Essential Linux Device Drivers" by Venkateswaran (Prentice Hall). Covers many things from how to build the kernel, to interrupts, dma, a/v, debugging, and many other subjects. I started to get into it, but set it aside when I lost interest in C, for more interesting languages like Haskell, Lisp, and Prolog.

Some how I doubt I'll ever get back into Linux kernel development; however, there is an interesting paper related to the House project (a Haskell-based OS), which describes a Haskell approach to low-level hardware interaction:

http://ogi.altocumulus.org/~hallgren/ICFP2005/

Microcontroller programming is also rather interesting... not because of the languages involved, but because it is rather cool to be able to program a full-fledged computer contained inside a chip that is only slightly larger than your thumbnail.