This is a series of tuturials for extending the interface possibilities of a computer with the Microchip PIC 18F452. I started with reading Dan O'Sullivan and Tom Igoe's excellent Physical Computing, and I would highly recommend that you get this book as a basis, as I may refer to it or assume that you know some things that it goes over. I also assume some basic knowledge of how computers work, like what memory addresses are. If you don't know that, I'm sure there are plenty of explanations on the web.
Physical Computing recommends various pieces of software that cost a lot of money. As a student and idealist with no money (I think no money is redundant there) I always try to use open source software. I found that there are very few resources for total beginners on how to do this sort of thing, so this will collect everything I found in one cohesive body. Maybe think of it as the GPL companion to Physical Computing. Actually, I did use MPASM and the MELabs Programmer software, which are free, but not GPL. I think GPASM would work just as well.
It is important to note that I tought myself everything here either from the web or books, and it may be vastly innacurate. I provide it only on the basis that it worked for me, which may have been dumb luck. I'm a technologist and a dancer, not a scientist; generally if something works that's enough for me, while a scientist would need to know why it works. If you're more experienced please read through and give me tips, both for my own edification, and so I can pass it on to others. Without further ado: The Open Source and Completely Wrong Companion to Physical Computing.
Shopping List Supplement
Basic Wiring
Beginning Assembler
Blink an LED: Hello World, PIC Style
Digital Input
Basic Serial Output