RAID setup can be a pain and if your not doing anything that is going to use it then as boonality said, no point. However seen as you ask, to setup raid you have to 1st turn on the function in BIOS, then make a RAID array using the a RAID manager, normaly accessed once RAID is enabled by pressing a certain F key or key combo during the boot up. Once this is done you need to load the correct RAID driver from a floppy disk when the M$ Windows setup process starts, that about it.
Back to your origional post, an OS claims needs 5-15 GB depending on what OS you use of install space but for it to run propperly, 50GB is a good allowance. Basically almost any SATA disk is going to be fine for it space wise as only the expensive SSD and some raptors dont have more then 50GB on.
BIOS should auto detect your drives
Your other 2 disks can be setup in no time using windows "computer manager" in "administative tool" under "Control Panel" you can format, parttion and asign your drive letters here.
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