i would say it is *not* true that 'most hardware is backwards compatible to 98'. Quite a lot of new kit just doesn't have drivers available for 98. It might or might not work. As to the chances of DOS being able to deal with the controller drivers.... Nill IMHO.
I gather this is a modern Abit AV8 motherboard. On my NF7 motherboard, the controller for the SATA drive looks like an IDE controller to Win2000, and I didn't have to load and special drivers for it when installing. In Device Manager under 'IDE ATA/ATAPI' controllers are two entries, one each for P-ATA and S-ATA.
Also, unless there is more than one hard disk there's no need to install the RAID driver, as there is nothing to build a RAID set with.
Win98 never had the 'Press F6' stage that I remember - I first saw it in NT4, then Win2K & XP. ME might have it.
The OP hasn't actually told us what he has tried. My suggestion is to simply install Win98. I suspect it will work. Once that is installed, immediatly install the motherboard chipset drivers. He might also want to visit the Abit site and check the Win98 drivers there.
Given, however, that the motherboard is one of Abits current models for an Athlon 64 so is a very modern board, in my view that a more suitable (modern!) OS than Win98 would be well worth while. It will be more stable and will support the new hardware much better - for example will the cool'n'quiet feature work under 98? As said elsewhere, Longhorn is *way* off and in my view going back all the time, given that some features are now being back-ported to WinXP...
A small note to the OP: next time, it would be very helpful if you include details of the hardware, OS and what you have tried so far in the original post. Clearly this is a much more tolerant forum than many, where the first reply would be to ask for all those details.. It's also very different to the Abit/AMD motherboard forum on this site where some people will tell you *all* about their hardware down to what colour the case is...
In fact - you might find that a more useful forum for getting the system up & running. There are *lots* of installation questions being asked there.