It's generally not a good idea to install your OS on a RAID partition.. you *are* going for RAID1 (backup), so I suppose it may be worth doing. To do it, you have to be able to setup the RAID at or around BIOS time which requires a real RAID card or motherboard with RAID support and some method of defining the array.
Once the array is defined, you'll simply install the OS on the SCSI drive that more recent versions of Linux *may* see.
If I were you, I'd install the OS on a non-raid partition, setup the drives as individual, then use a software RAID in Linux to create your RAID (in which case, the type of mobo you have really makes no difference... though, in your case, that's not much of a concern being that it sounds like your mobo doesn't really do hardware RAID control anyway).
Doing it this way is pretty easy... there's plenty of documentation on it - look at fdisk and "Linux Software Raid" in google. If you want to be lazy, software raids can be setup easily with Webmin.
Of course, if you want performance, go out an buy a real hardware controlled RAID card from 3Ware. Stay away from Promise.