http://en.wikipedia.org/wiki/OS/2
Basically IBM's vision of OS/2 wanted to close source it strictly to IBM machines, and Gates wanted Windows 3.0 to be an open hardware OS, independent of manufacturer. Also Windows 3.0 was more device driver friendly, more future proof, and application friendly than OS/2.
Gates didn't hijack, sabotage, or steal anything from IBM. They had a business relationship, they had a strategic differences, and they parted ways soon after. IBM screwed themselves in this regard, OS/2 was closed off and blew chunks, and them failing had nothing to do with Gates.
IBM and Microsoft signed a joint development agreement in 1985 to co-develop OS/2 as a DOS successor, which the latter broke in 1990. The primary reason was popularity of Windows, which at that time was a simple graphical add-on to DOS, inferior to OS/2 but easy to use and compatible with the huge base of legacy DOS software. It was sheer profit from Windows that made Gates break the agreement with IBM, not their "strategic differences" or whatever else is written in Wikipedia.
You're letting your unwarranted hate for Gates cloud reality dude. IBM has always been IBM's worst enemy, not Gates. Instead of trying to fault Gates for the downfall of IBM's OS business, see history for what it is. IBM is always behind the tech curve when it comes to innovation and opening it's architecture behind closed doors:
http://www.nasdaq.com/article/4-ibm-blunders-that-gave-big-blues-competition-the-edge-nyse-ibm-cm443432
They basically handed the OS monopoly to Bill Gates, they have no one to blame but themselves...
Yeah, haters gonna hate. Personally, I don't care about Gates, but I could just tell you the same, i.e. see history for what it is. Microsoft entered an agreement with IBM (do you deny this?) for co-developing OS/2 (don't think of this system as IBM's project only, both companies agreed to develop the new system), and Microsoft continued to develop Windows at the same time. When Windows turned out to be more profitable in the end, they just abandoned OS/2 as being Windows direct competitor.
Indeed it was IBM's fault that they didn't expect Bill to switch sides!