If I remember rightly Windows 2000 wasn't aimed at the home user but more at businesses, ME was aimed at the home user back then, and it was the worst Windows ever.
We use Windows 2000 at work and I can't really compare because it's set up so shitly compared to my XP machine.Overall I think Windows 2000 is better than XP home though I don't know about XP professional, I often wish my PC had been shipped with XP Pro because it has better security and configureation tools, i.e. it's more like NT should be it's not as cripple with all the bullshit.
I don't know much about the MS OSes of last 10 years or so but when MS first released Windows 95, they carried on supporting 3.1 for awhile. You also had a choice between Windows 96 and MS-DOS 6.22 with Windows 3.1 when you bought a new for a year or two after.
I can't remember this happening with Windows 95, 98, ME XP, this is probably because 95 and 98 were very similar as was ME which was the worst of the three. I suppose when XP came along it was so much better you would've been stupid not to have accepted it.
I hope people are given a choice for at least the first year or so when Vista comes out then if it's shit it'll fail but if it's really that bad and they're not given a choice then they just won't bother buying new PCs.