> Windows NT was based on UNIX
Bits of MS-DOS 2.0 were based on a casual understanding of unix.
Win NT 3.5 is, frankly, the IBM/MS OS/2 project after IBM and MS stopped working together on OS/2. Protected (really large-memory) Mode, Presentation Manager (early GUI windowing, based on MS-Win 2.1). Mostly clean code. No more "unix" than any other serious O/S of that time. As JDB says, there's as much VMS as unix/Xenix in there.
NT 4.0 (the one most people know) is fairly good, if austere even compared to Win95.
Win Server mostly descends from NT core.
Windows 2000 is redecorated NT4. The TCP/IP stack for Win2000 is apparently a direct take from one of the open-source unix projects, which gives W2K a much more robust networking.
XP cleaned up some loose ends in W2K and added many frills. W2K would still be viable, except support is ending so any newly discovered XP/Vista bugs that hackers can exploit will not be patched on W2K.
Win Server 2003 is a striped-down Win2000 plus a few add-ins. VERY solid machine.
Vista is, I think, a major redecoration of XP. I used it for a week and lost interest. Everything is more pastel, everything is in a different place. "easy, cute and bubbly". Sometimes, the changes make perfect sense.... AFTER you stop looking in the places they used to be. Some changes are potential improvements: the Mail program is a complete winner, the only mailer I ever used that might take me away from NetScape/ThunderBird. The network wizard figures out many common network situations without user action. (But un-common networks can be a real hassle to set-up.)
People who don't know any better use Vista without complaint.
People who know XP well get very frustrated in Vista, and whine about it to all their friends. So it got a bad rap.
Vista has been out for 2 whole years, but seems to be on only 20% of PCs. Since most folks out-grow or corrupt their PCs every 2 to 4 years, we'd expect a lot higher than 20%. There does seem to be reluctance to move to Vista. And since you get Vista on new PCs, that means new PCs are not selling well.
All this 32-bit versus 64-bit is meaningless to most users. It won't be important until we all have >3GB of RAM. That day is coming quick: I have 1.5GB in my flaptop and MS Live Maps 3-D was trying to use all of it, just to display one fuzzy map.
I lived through every Mac O/S from 2 through 10. Mac has been MUCH more busy putting familiar things in new places in every new release. The MS network dialog hardly changed from NT4 to XP, which Mac was changing all the time. And I've also loaded dozens of Linuxes. While a bare unix box has a standard place for network settings, GUI versions all use different GUI helpers hidden in different places with different permissions.
I've avoided loading Vista, because I know XP and it is good enough. I sigh when I'm asked to help others with Vista, but it's just "different", not "crap".
It isn't too clear that Vista -needs- more resources than XP. I dabble in tiny machines. A fair number of them, users report that they run XP OK but run Vista as good or a bit better. Yes, a full-feature Vista can absorb all the hardware it finds, so skip the Aero dizzy-desktop and other options.
I'll be testing Win 7 soon. Early comments are positive. If I feel better about it than I did about Vista, that will guide my going-forward plans: buy new PCs with Vista (getting new PC with all XP drivers is becoming hard); or put a cork in upgrades until Win7 is published.