If you are willing to spend $100 or so you can get a very decent backup. Grab one of the USB or Firewire connected external drives that have retrospect backup bundled with them. Schedule a daily incremental backup around the times you aren't using the PC (sleeping or at work and such)
Any raid OTHER than Raid0 is simply fault tolerance, not backup. If a drive fails, you aren't Fudgeed and can continue operating w/o shutdown until you replace the dead drive... unless you have hot swappable drives

Raid doesn't protect you from accidentally deleted files and viruses... daily backups do. Raid reduces the impact of hardware failure only, backups reduce the impact of user failure and hardware failure.