in practice, raid 0 is almost twice as fast as a single disk, but if *either* disk fails, you lose the data on both.

raid 1 usually doesn't offer any performance boost at all (and can sometimes be slower - even though the bus should work in parrallel, it has to push twice the data on writes) but if a disk fails, you have a backup on the other disk.

if you have a way to do backups (a big ide disk or another machine on your network) go for raid 0, but if not you are probably better off with raid 1.

if you want both reliability and speed, you'll need a card that can do raid 5 on 3 or more disks.