If you switched computers, you might be missing the internal connector from the CD drive to your sound card. (Or you might just have the CD volume muted in your audio mixer.)

Are you able to play an audio CD using the cdplayer application included with Windows 98? If your CD-ROM drive has a headphone jack on the front, can you hear anything if you plug your speakers into that jack?

If all else fails, I've heard very intriguing things about _inmm.dll, but that really shouldn't be necessary under Windows 98, I would think.

(By the way, don't forget that the long-lost expansion pack was released as freeware when it was unearthed a few years ago.)