|I'm guessing that the old mboard did NOT have onboard video.|
ATI Rage 3D IIC is an OLD video chipset - it probably first came out before 1998.
It has to be on either a PCI or an AGP video card.
I have an older PCI video card that also has an OLD ATI video chipset - Rage XL, on an ATI Xpert 98 card, which also supports 3D graphics. I bought it years ago so my nephew could play games that have 3D graphics on an old computer with a max P133 mboard with onboard video that I had upgraded with an Evergreen Spectra cpu adapter that has a K6-2 400 cpu. The Rage XL video chipset cannot tolerate being installed on a mboard that has onboard video, because the video chipset was never designed to co-exist with onboard video. It will work properly on a mboard that has onboard video ONLY if the mboard has a jumper that can disable onboard video. Some 386 and 486 mboards have such a jumper, but only a few really OLD early Pentium mboards have that jumper. Newer mboards do NOT have such a jumper.
The problem is both the Rage XL video chipset and the onboard video try to use some of the same resources when the Xpert 98 card is installed. When you have that situation, either the card produces no video, or my case (in Win 98SE) the video from the card is a jumble of video from both video chipsets.
After spending many, many, many hours fiddling, and discovering a non-standard way of installing the card, I managed to get the card to work in 98SE, I had to disable the onboard video in Device Manager, but then I found I could not load newer video drivers that were available for it. Later on, my nephew installed XP on the same computer, that went much easier, but I still had to disable the onboard video in Device Manager, and I STILL could not load newer video drivers that were available.
The bios on mboards that have onboard video assumes that the video chipset on the video card you're using in a slot can co-exist with the onboard video chipset. If the video chipset DOES support co-existing with onboard video, then both video chipsets can work. If the video chipset is on an AGP card, and the mboard has an AGP slot, installing an AGP card in the AGP slot almost always automatically disables the onboard video - the settings in the bios for Primary video or Intialize video first or similar cannot disable the onboard video by you merely selecting something other than onboard video in those settings - the only thing that's useful for is to inform the operating system which video is the primary video. If you set that to onboard video or PCI video and your video card is AGP, Windows will not be able to use the advanced AGP features of the AGP card in Windows - that has to be set to AGP in the bios for an AGP video card. Similar applies for a PCI-E video card.
If the video card is PCI, the settings in the bios for Primary video or Intialize video first should be set to PCI, to inform Windows your Primary video is PCI, if that's what you want to do, however, installing a PCI video card usually DOES NOT disable the onboard video automatically, and almost always, you can't disable the onboard video in the bios by any setting either in that situation.