broadwayblue, the KT7 RAID support is for the IDE channels. There are 2 ATA/66 and 2 ATA/100 I believe.
RAID-0 is striping, which lets you "stripe" drives 1 and 2 of size A and B to have them act as one drive, of size A + B.
RAID-1 is mirroring, which "mirrors" drive 1 to drive 2. Anything written to drive 1 is written to drive 2. This is typically used for servers for obvious fail-safe reasons. Reads tend to be quicker, writes tend to be slower.
www.tomshardware.com has an excellent article on an old Promise RAID ATA/66 controller that explains the different levels more in depth. It also describes RAID 0+1, or RAID 0,1, and anything I may have forgotten. Just search for "RAID" on that site.
As far as advantages, that depends on your setup.