spannersatcx,
The whole point of RAID is to run two drives either as Striped (For Performance) or Mirrored (For Reliability).
I mentioned 7,200rpm Drives, but Raptors are even better, as goates mentioned. (Raptors are at a premium.)
With the current pricing on the WD 7,200rpm SATA Drives, it is very little to add the second HD and you get the added boost of RAID 0. (And for kids, it is something to boast about, the "Coolness Factor")
Take Care,
Richard