Try to setup a windows 98 machine as a web server and see how it goes (Windows XP only came out in 2002). It doesn't do HTTP/1.1 so it's good question whether clients would be able to connect at all.
Windows 98 was a client OS, it was never intended for this. A proper test would be Windows NT 4.0 Server. Or more realistically for the time frame, Solaris 7 or 8.
Obviously forget about any security.
When you're running a server, TLS is not the only service you are dependent on; you're also dependent on security updates. If they're not backported, you'll need to make version upgrades.
Arguably it's better to think of every piece of software running on a server like it's a service, to maintain security and performance in an Internet full of hostile actors.
I don't even understand the mindset of wanting to run a live server on ancient software, aside from doing it as a hobby. In which case, it's pretty typical for such hobbies to require extra work and care. Driving around in a car from 1940s takes more maintenance work, and is less safe, than a modern car, and everyone gets that.
Of course, I was rolling my own query sanitizers, which was the style at the time; and my php.ini did allow GET/POST to inject global variables. Not to mention CVEs discovered between now and then. So I wouldn't want that server from year 2000 to stay running untouched, but win98 is a strawman.
Could have been yours ;)
Just so you know, Windows 2000 is vastly more stable than the 9x branch and is perfectly usable, so you should upgrade.