Win9x was known as platform 1. NT is platform 2.
So Win98 was v. 4.1, platform 1. WinME was v.
4.9, platform 1. NT 4 was v. 4, platform 2. Win2000
was v. 5.0, platform 2.

WinME was a flop, which was actually convenient
when MS tried to push people to XP. WinME was
almost new when XP came out, so it didn't make
much sense to say it was obsolete. What MS did
instead was to pretend ME never existed (as they've
done with Vista) and then talked about upgrading
the "obsolete" Win98 to XP.