VDMSound runs practically all DOS games on NT based Windows.
AS a bonus, you get to use USB game controllers, too. I've had great success in running such classics as Red Baron and GP2 on my XP Home SP2 system.
AS for the thread's question... I'm using Windows XP Home SP2, but I also have Kubuntu 6.06.1 LTS "Dapper Drake" installed - Edgy didn't, for some reason, recognize my wireless keyboard and mouse after I installed it, so I'm staying on long term support version.
I'm mainly using Windows, basically because I can only get stereo sound out of my external SoundBlaster Live! 24bit sound card, and "only" four-channel sound with my onboard Realtek AC97 soundcard. I know that is in fact better than many ever get out of Creative card (or onboard for that matter), but I really want to actually use my hardware as it was intended to be used... It's not fun to own a 5.1 speaker system and 5.1 capable sound card and run them on OS that can only use 1/5th of their capacity or so. It would not be an issue if I used standard 2.1 speakers, or a headset, but...meh. So I'm running Windows to:
-play games
-listen to music
-watch movies and stuff
...what's left? I can use GIMP better in Linux than in Windows, and OpenOffice is at least on par with Microsoft Office (Without the annoying speaking paperclip of doom, and without as many annoying auto-edits). I can also use Internet in Linux without any problems.
The trouble is, I can also do those very well in Windows anyway, and to use them in Linux I would have to boot into other OS, which takes time, regardless of how much faster Linux starts than Windows.
That brings me to another interesting thing. System speed.
I used to have a 64bit edition of Ubuntu Dapper, but it was like hell to get things like Opera or Flash working. It could be done, but I simply fed up with having to play around with chroot... and the sound didn't work any better, unsurprisingly. So now I am slightly more happily running 32bit Kubuntu/Ubuntu/Xubuntu (havent't decided on my favourite desktop environment yet, although KDE feels better than Gnome or XFCE to me). I haven't noticed any immediate speed changes, and things got whole lotta easier for, say, playing Windows media files and DVD's. Not that I would actually want to watch DVD's with half-assed, semi-functional sound system anyway, to tell the truth.
Obviously Windows has its annoyances - like requiring about the same time as a nuclear power plant to start up, explorer.exe sometimes being more than a little sluggish or even collapsing altogether (Heck, I don't even have it running half of the time for that exact reason), or having to boot the whole system when it simply stops responding, whereas in Linux I (usually) only have to Ctrl-Alt-Backspace the desktop environment. And Linux is in overall more carefree system to use Internet with, for obvious reasons.
I would very much like to move to using Linux for watching movies and listening to music, as that would enable me to use Linux for perhaps 95 per cent of the time. Last 5 % I would run Windows to play Pacific Fighters or Rome: Total War. The third game I'm playing is Freespace Open, and that I could run in Linux rather well - if the sound wasn't b0rked in that, too. The sound effects were always about half a second late on my 64bit installation. It was okay, but slightly distracting in some situations.
So... it's mainly sound problems that keep me using Windows despite the alternative. In my view, the Linux installation is kinda "backdoor" to use if Windows installation gets somehow screwed up by a spyware, virus or any (other) crap that Microsoft calls "a feature".
If I would only use my PC to do some office work, use Internet services and simple basic stuff like that, Ubuntu (32-bit) would be my choice for sure.