I know this is an old post but ...
It appears the the waters were extremely muddied by the fact that Realtek posted a driver that doesn't actually work in Windows 98 (not on my system anyway) even though the download page clearly says that it supports all Windows versions from 98 Gold to XP!
The second fault condition, with the error in the Device Manager resources tab, was caused by the faulty driver.
The original fault, where there was no error in DM, but just no sound, seems to have gone away now I have cleaned out my system.
For anyone else with a Realtek AC'97 sound system and Windows 98, beware!
Version 4.00 works, version 4.06 (the latest posted) doesn't.
I have informed Realtek of this, I'm not holding my breath while waiting for a reply!
I have the same (?) situation with a GA-8IEX Rev 2 motherboard that I'm trying to get going. I initially tried the Realtek drivers from Gigabyte, which correspond to version 4.06, then found this post and tracked down a copy of the 4.00 drivers. So basically, I uninstalled the 4.06 drivers via Add/Remove Programs in Control Panel, then installed the 4.00 drivers.
Now, the drivers are installed and report as OK, but there is no sound. So, did you need to do anything special to retrograde these drivers (or do I have faulty hardware)?