I have Windows 2000 Pro and it hasn't crashed... well.. for a very long time. I believe it's not so much the operating system that you use, but the software you put on it that will determine how stable it is. No matter what OS you use, it can be potentially unstable if you put lots of **** on it.
Of course there are always exceptions. Windows ME is the exception. :D Stay away from it and you'll be fine.