It's very cool... there are a ton of free textures on Flickr and various blogs (check out Skeletalmess at http://www.flickr.com/photos/skeletalmess/collections/72157615670287235/ and Shadowhouse Creations at http://shadowhousecreations.blogspot.com/).
A big thankyou to both of these sites... the postcard textures used here are from the Shadowhouse Creations blogspot.
OK, get to the point... a texture is basically a photo of anything... stucco, cement, old paper, blank post cards, whatever, that you blend with your original photo. It changes your original photo in really interesting ways. I think I might like to do a series of old postcards of desert homestead cabins... I certainly have a lot photos to use, and I like the old-timey look!
Anyway, here are my first few creations using textures. Stay tuned, more to come!