Ed Durrant added:

A mixture of OS/2. Windows 98 and Windows NT4 were used, in the previous winter games at Nagano it was almost all OS/2. The key point was that without OS/2 none of those systems would have been built and operational is the same time frame. As well as running critical back-end systems, the complete system build processes depended upon OS/2 Warp Server systems. The commentator information system was totally OS/2 with touchscreen terminals for reporters of the various TV companies at the games. There were actually a couple of HUGE mainframe systems and several midrange systems analyzing and feeding historical and timing information to other systems.

The actual reason that IBM got out of the Olympics was that the International Olympic Committee (IOC) wanted to go back to the same disastrous model used at Atlanta - having multiple IT companies involved as they believed they could get more money that way from sponsorship from the companies. Atlanta proved this does not work, each company had to seamlessly interface with the others and commercial pressures simply stop them from working together (or that's a nice way of putting it).

With Sydney 2000 IBM was the sole responsible IT provider and companies such as Kodak (photo-IDs), Fuji-Xerox (Printing) and Swatch (timing), were all sub-contractors managed by IBM. The result was that the Sydney 2000 Olympics were the best organised Olympics to that point (I cannot comment on later events as I have not been involved with them as I was with Sydney 2000).