Here's a neat ebook/website on how to make your own x86 operating system: The little book about OS development by Erik Helin, Adam Renberg.
For anyone who was ever curious about what it would take to make their own OS, this looks like just the thing.
This text is a practical guide to writing your own x86 operating system. It is designed to give enough help with the technical details while at the same time not reveal too much with samples and code excerpts. We’ve tried to collect parts of the vast (and often excellent) expanse of material and tutorials available, on the web and otherwise, and add our own insights into the problems we encountered and struggled with.