I did not really forget win2k.
Win2k was part of the NT line (corporate line) of windows.
First there was DOS then you had 1.0 2.0 and 3.0
Then you had windows 3.1 for home users and windows NT 3.1 for corporations.
Windows 95 for home users and Windows NT 3.51 for corporations.
Windows 98 for home users and Windows NT 4.0 for corporations.
Windows ME for home users and Windows 2000 for corporations.
While the home versions of windows were based on Ms-Dos, the NT line was using a different infrastructure which proved to be much more stable.
Microsoft decided to release a revamped version of Windows 2000 incorporating the new features for home users which they introduced in windows ME.
This was released as Windows XP in both a home and professional version.