If you're looking for a NAS with room for plenty of disks that's also fast and user-friendly, then the new Synology DS-1512+ and DS-1812+ are two models that should be on your wish list. They come equipped with the very comprehensive DSM 4.0 firmware, with space for either five or eight hard disks. You do have to reach pretty deep into your wallet for these NAS devices.
Slow computer got you down? Maybe a hardware upgrade should be in your cards, if so this guide to the Fundamentals of Upgrading a PC is an invaluable read. PCSTATS Tips