i have been running Win2000 for 7 years and have had no complaints. the OS doesnt have the XP-like "wizards" that make configuration of hardware simpler, but if you know what you're doing, you dont need that. Paint.NET (free image editor) is the only prog i ever tried to install on my Win2000 box and ended up not being compatible with the OS.... but even that prog, at any version prior to 2.7, runs fine on Win2000. from what i remember, Win2000 was the first time Microsoft got highly praised for an OS release. Win2K is both stable and well-supported.
i chose to skip WinXP because, im my opinion, its eye-candy didnt justify the investment.... and because of the rumours about the small footprint of the future Windows 7, i've decided to skip Vista too. nothing can beat stability, speed and compatibility.