Vista was the direct next level of Windows after XP. It was an
official product and should never be "ignored."
Millennium was a "feeble" attempt from Microsoft and appeared at the
same time as Windows 2000.
Back in those days, Microsoft had two different lines of Windows
operating systems. The NT line was the Professional line and the 1.x,
2.x, 3.x, 9x line was the home user line.
Windows Millennium was the last product in the home user line. Despite
the change of name, it was essentially just the last version of
Windows 98.
Windows 2000 was the first version of the NT (professional) line that
had no number. It followed Windows NT 4.0, and under the hood it was
NT 5.0.
After Windows Millennium, there were no further releases in the home
user line. Everything afterward was in the NT line, which became more
oriented toward *both* professionals and home users. So, under the
hood, Windows XP was NT 5.1, Vista was NT 6.0, and Windows 7 is NT 6.1
