Buying 80's to RAID just isn't worth it unless you are talking about 10k rpm drives or SSD's as otherwise they will be very slow. A single 6401AALS will be faster than 2 standard 80gb drives in RAID-0 not to mention cooler, more reliable and more space.
RAID works great, but its still only as good as the drives you raid. With good software raid you get almost the same speed increase as the number of drives you have. For example, my 3x 500gb drive array runs at 2.75 times the speed as one of my drives does by itself.