If you're tired of leaving your PC on continuously so that other machines in your house can access the files you store on it, you're ready to step up to network-attached storage. As you might guess from the name, NAS devices connect via ethernet directly to your router.
Your network storage device can be a stand-alone unit designed specifically for centralized storage, or you can convert an old PC into a file-sharing device. Either way, you'll have a 24/7 data repository for backups and for sharing documents, images, videos, and other files.
A NAS device should be isolated in a safe, cool, dry, out-of-the-way place to make it less vulnerable to bumps, spills, and other physical dangers. (Plus, hiding your storage device keeps it safer from theft.) Though off site is the safest destination for your backups, NAS can be the next best thing -- barring tornadoes, tsunamis, and other acts of nature.
NAS boxes are isolated from most of the software dangers that networked PCs fall prey to, as well: Even if the files stored on a NAS device get infected, the box's operating system resides in its firmware (unless you're using a retasked PC), and is therefore very difficult to attack.
Dedicated to storage
Nearly every PC under four years old supports gigabit-per-second ethernet. If yours doesn't, spending $US20 or so for a gigabit ethernet adapter is a good idea. With gigabit ethernet, a movie streamed from a PC or NAS box looks as smooth as silk, large files transfer at blazing speed, and backups are far faster than with older 10/100 ethernet cards, which are limited to 100 megabits per second (note that these are theoretical speed limits; real-world speeds are slower). That said, my old reliable 10/100 500GB Maxtor Shared Storage Drive still manages the small-scale backups for my office network.
Gigabit ethernet is not a perfect solution, however. Router vendors have been focusing on boosting the speed and reliability of their wireless networking gear. Only a few pricier wireless routers -- such as the $US150 D-Link DGL-4300 I've used for the past year, D-Link's $US180 DIR-655, Netgear's $US160 WNR854T, and Buffalo's $US250 WZRAG300NH -- include a gigabit-capable ethernet switch. Some NAS boxes can connect wirelessly, but they transfer data at a considerably slower pace than a cabled connection does.
Linksys's WRT350N pre-N wireless router (about $US170 online) has a quartet of gigabit-ethernet ports, as well as other features that make it an alternative to a dedicated NAS box. The WRT350N sports a USB 2.0 port to which you can attach a normal USB hard drive, effectively turning the router itself into a NAS controller.
The WRT350N, like the Iomega StorCenter and Maxtor Shared Storage II, also functions as a Universal Plug and Play (UPnP) server to stream photos, MP3 files, and movies to your PC, TV, stereo, portable player, or other playback device equipped with a UPnP media adapter. Like gigabit ethernet, UPnP is an important feature to have if you're planning a home multimedia network.
For even more flexibility, get a NAS box with USB ports for attaching a printer that you can share across the network or for expanding the network's storage capacity via standard USB hard drives. With a high-end NAS box, you can back up your network storage by attaching a backup device directly to the box, rather than having to go through your PC. Most people, however, will store the backup of their NAS box on DVDs, or on a hard drive or tape drive attached to their computer.
Another option: Buy a NAS enclosure that lets you plug in your own hard drive to build a NAS box with as little or as much storage as you can get on a drive (or two, for enclosures that support multiple drives). Tritton's $US100 TRI-NSS001 NAS Enclosure works with any 3.5-inch ATA drive and supports up to 400GB.