Sure. A SAN is a Storage Attached Network - a very sophisticated system of disk drives and controllers that send data across a dedicated storage connection to your servers, typically fiber optic. Think of it as a dedicated type of network for storage. You can, in fact, even buy SAN switches that allow a bunch of machines to attach to the same set of disks (although typically on different sets of volumes).
NAS is Network Attached Storage. It has similar components, except the communication from your server to the drives occurs across an Ethernet network instead of a dedicated storage network. This provides more flexibility (i.e. physical proximity isn't absolutely required, multiple NAS devices can communicate between themselves across a network for DR data synchoronization, etc.). Most enterprise-class (like you'll need) NAS devices can also be SAN-attached, too. This is especially good for storage, as most high-end backup systems can be directly SAN-attached so that backups don't have to traverse the network.
IMHO, I like NAS better for the typcal admin. SAN is a whole different language and environment, NAS tends to be a bit easier to understand and deal with.
One other thing you're going to have to spend some major cash on is backups. For a dozen terabytes, it's going to take a really big library and some careful thought on managing the back strategy, etc. Need to look at something like a StorageTek L180 or a big ADIC.
- G