Go NT and hardly ever crash!!!
I run NT for my mastering software. It is very stable, and things run very smooth.
I don't think that with any Service Pack after 4 that you need to worry about finding any DirectX drivers or any of that because usually the Service Packs provide these kinds of upgrades. SP 6 as I recall is a decent Service Pack. 5 was a whole other story.....

I am running SP 5 on my NT install and I can run most any audio application and/or DirectX and VST plugin's with no problems at all.
Don't worry about getting audio software that will run on NT, most of it does.
You should be worrying about a soundcard though. You will find that it is very hard to find the more popular 8 in 8 out soundcards that have NT device drivers. Even when I was just looking for a 24 bit 2 in 2 out soundcard, there was only really two on the market that were any good that have NT drivers, the Card Deluxe, and the Lynx One card. I went with the Lynx One card.
I actually prefer the non-Plug and Play feature in NT 4. Plug and PRAY doesn't always work so damn well, and it is a pain in the ass to have the OS wanting to install device drivers after booting up. It is very easy to install hardware in NT, you just run the setup program that usually comes with the hardware. Very straight ahead, and actually, NT seems to assign it the proper IRQ's and all that quite well. I have far less issues installing hard ware on NT then I even do on 2000.
Do yourself a favor. Get NT. So what, you can't play games on it. But, you can record all day without your OS freezing up on you or just crashing hard every 10 mins!
Good luck.
Ed