Depends on what way you want to go. If you want more internal capacity, mega's suggestion is the way to go. The Netgear solution you linked does not include the price of the drives and runs $60-100. An internal 2-port ATA or SATA card can run as little as $15 online.
Installing an add-in card is not complicated, and if you're running Windows 2000/XP, it should recognize it without you having to install any drivers. If you want to share your files, the Netgear Z-NAS might be the way to go if you don't want to share off your PC, or have files available and still shut your system down.
Personally, the NAS is probably overkill for you, unless you don't have extra spaces for hard drives in your case.