Raid is server tecnolgy,it is usefull for the home user but I opted to pass on it.I am unfamialar with it and that is the reason I stayed away from it,also it is new to the home market so you may want to read up on it and let people with it tell you what thay use it for.
You may be able to use one HDD if you go the Raid mobo route, and only use the IDE headers, and disable raid...but, if you use the raid headers, you have to have 2 drives of equal size and speed. Several of us are trying to get some raid boards going as 8 IDE headers instead of doing it the raid way.
I suggest getting the board with raid available on it. Even though you do not plan to use it at this time, expandibility is always a good thing...'ey? Not only that, when you do acquire the lettuce to bust out another (same size, same model, same interface speed) HDD then you will have twice the room, and pretty much twice the speed. And that's always a good thing. ;D