Both technologies create disks that are accessed directly by many computers over a wired or wireless network. The computers share the network resource. This reduces maintenance in large systems, and also avoids having a single computer tied up answering requests for its data from all over a network.
Storage Area Network disks run as an extension of a computer's operating system. Therefore connected computers must have operating systems and software that are compatible with the Storage Area Network to be able to use it.
A Network Attached Storage is a more complicated device that has its own, small operating system. Sometimes computers that have been converted just to be file servers are referred to as Network Attached Storage devices
There are a number of options for network storage. One of the cheapest options is the Netgear SC101 Network attached storage devices. The Negear SC101's cost about £60 and you just fit up to two low cost IDE hard disks inside and you are pretty much ready to go.
For more details on the Netgear SC101 Storage Central