MY WIN98 installation is almost back to normal. I pulled the DC10+ video capture card, let Win98 detect the Adaptec SCSI card, and Win98 very nicely stuck the Montego sound card back into IRQ5. Then I shut off the machine, re-inserted the DC10+, and when I booted again, there it was, happily sharing an IRQ with the PCI to USB Universal Bus Controller.
But IRQ 3 is still unused. And my DSL card is sharing an IRQ with my TNT2 Ultra. Why, oh, why?
The DC10+ is also seems a little jumpier on playback than it was, so I may have to fool with my disk parms again, but it's working, at least.