Well, actually Microsoft bought up "QDOS", developed by someome else, and sold it to IBM, for their new PC.
There is a rumor about a failed meeting with IBM ambassaddors <img src="/ubbthreads/images/graemlins/winkwink.gif" alt="" /> and the head of another company which made the OS CP/M (sorry, but I've forgot the name. It was something with "digital"). Thus Microsoft got their brand-new bought OS into the PC, and not the other company.
Besides that, I've once seen a quotation that was said to be from Bill Gates' own biography, saying that he was fishing bad ideas out of peoples dustbins for considering (and maybe later use). <img src="/ubbthreads/images/graemlins/winkwink.gif" alt="" />
