that's an interesting question and it has intrigued me :)
On the windows 98 machine I presume you have some kind of dvd software installed. Well, here is the sequence of events that I would try...
1. share the dvd drive across the network.
2. map the network drive on other machines with
a drive letter.
3. Install dvd software and point it to the
letter you assigned to the drive.
Please let us know if this works
If you dont have any dvd software, checkout the microsoft site for the latest version of media player as Im sure this supports dvd. On my XP machine I have licensed and installed XPack which runs dvd like a dream in media player