The 2800 was designed as the first step of 2700 to 3700 migrations, so restaurants that couldn't afford a full upgrade in one shot could hold onto their terminals and still get the 3700 backoffice features. It was never meant to be a long term solution, so after the first few service packs that stabilized it development was basically non-existant and it was never updated to support running on w2k.
From what I remember, 3700 v3.1 was the first to be officially supported on w2k. v3.0 could be loaded with a registry hack but Micros support wouldn't touch them, and nothing below 4.0 will run on XP/2003.
NT is well past end-of-life and is tough to get support on, but it's a workhorse. If you're not having problems stick with it until you're ready to change the whole system and use a 3rd party compliancy solution if you run credit cards through the system. Even if you can hack your way into running it on w2k you may have a tough time getting support, and the current products all require XP or 2003 so you'll have to upgrade the OS again when you go with a new system.
One concern about staying on NT, or even w2k for that matter, is virus protection. If your Micros servers have internet access you should probably make sure you have a good solid firewall. There are a bunch of viruses floating around designed to take advantage of security gaps and invite others to join the party. We found out about this the hard way, and believe me, these things are like Paris Hilton and Linsey Lohan; no matter what you do they just won't go away.
