Maybe I'm wrong, but didn't Palm buy Be Inc.--the makers of BeOS. I've run BeOS once, and hate it. While some peole like it, I really doubt it's a really viable source.
My personal opinion is that Mac OS X is probably the best shot for a viable Windows replacement. After Windows, the next OS that gets software or driver support is the Mac. Companies rarely produce drivers themselves, and if they do, it's rarely supported. The Mac gets a Unix backbone, but retains a user friendly interface. The l33t h4><0r types can do their thing if they wish, but it's not required. People are generally intimidated by computers to start with, and Linux is not very helpful to ease this, if any. If developing continues for x86, I really think that it would be a serious alternative to Windows. Linux is cool until you realize you don't know what the hell to do with it. I've had a change of mind toward Linux over the year, and unless some major changes occur, it will go the way of OS/2. I'm all for alternatives, but I haven't seen anything that is believable. I'm certainly looking for something to jump to as Microsoft doesn't seem to get the concept of "user friendly". XP is a real yawn to me, nothing I want to deal with or need. I'll stick with Win2k for now, unless MS stops their policy of leaving strings attached among other things.