The fact that the DVD was made with Win98 shouldn't be a problem. The DVD standards haven't changed... If the DVD was standards-compliant before, it's still compliant now! (I'm assuming this is a "regular" video DVD with VIDEO_TS and AUDIO_TS folders?)
My first thought is that the DVD might be scratched or damaged. Or, there's something else wrong with the DVD... It may have been a flakey/defective blank, or a bad burn. (Some players are more tolerant than others, so you might not be aware of a problem.)
Try dragging the VIDEO_TS folder from the DVD to your hard drive. If that fails, you've got a problem with the DVD or your computer's DVD drive.
If the folder does copy OK, try playing from the copy on your hard drive. And if that works, you can try burning from the hard drive to a new DVD. (Copy and burn the empty AUDIO_TS folder too.)
You can also test the DVD (and your drive) with
Nero CD-DVD Speed (FREE!!!).