yes you can stripe two SATA drives together in a RAID using Apple Disk Utility. You can actually stripe 4 SATA drives using wiebetech's G5 Jam...but it doesn't help you run multiple movies any more smoothly. It's more of a seek time issue, how fast the read/write head can whip around reading bits of 3 or 4 movies a bit at a time. Imagine a record player's needle jumping around trying to play 1 snippet of each of 4 songs before it had to go read a snippet of one of the other songs....

then you get an idea of what your hard drive is doing.