These days its not uncommon to own two or more PCs, and if you have family members under the same roof, they probably have their own machines as well. Why not create a "backup network" that leverages everyones hard drives? All you need is the beta of SyncToy 2.0, one of Microsofts free PowerToy utilities. With it you can create "folder pairs" between PCs, copying files between them with a single click. This is a great way to sync, say, disparate photo libraries between your PC and your spouses, and create a backup of both in the process...SyncToy Download Page

From the Microsoft Site:

SyncToy, a free PowerToy for Microsoft Windows, is an easy to use, highly customizable program that helps users to do the heavy lifting involved with the copying, moving, and synchronization of different directories. Most common operations can be performed with just a few clicks of the mouse, and additional customization is available without additional complexity. SyncToy can manage multiple sets of folders at the same time; it can combine files from two folders in one case, and mimic renames and deletes in another case. Unlike other applications, SyncToy actually keeps track of renames to files and will make sure those changes get carried over to the synchronized folder.