I am not sure of the exact way sata works when you also have other ide drives...
maybe there are things in the bios to choose as to which one to boot off of first etc...
RAID= redundant array of Inexpensive disks....basically it is a way to group drives together for certain advantages.....if you dont know if you are using raid..then you arent,lol...there are extra steps to setup raid etc.
here is a great raid article..or rather some cool pictures describing different types of raid setups
http://www.acnc.com/raid.html
for home type setups, RAID 0 and RAID 1 are most popular.
JP