How can I put photos in a frame with text on a Mac

[Apple fanboy]

How can I make a picture like the one below with text. I know how to add text to a picture using preview, I'm just not sure how you get a series of photos like this. I see it in a lot of places so I'm guessing I just need the right app or instructions! Using Mountain Lion if that helps. Thanks for the help.

 

[CrickettGrrrl]

How can I make a picture like the one below with text. I know how to add text to a picture using preview, I'm just not sure how you get a series of photos like this. I see it in a lot of places so I'm guessing I just need the right app or instructions! Using Mountain Lion if that helps. Thanks for the help.

Two ways off the top of my head:

Pixelmator for $15, here's a collage tut:
http://www.pixelmator.com/tutorials/photo-collage/

or use iPhoto for free.
Select the photos you want, then hit the "Share" button on the bottom right, then choose email, then use the templates. I'd arrange things using full screen mode and then take a screen shot. The iPhoto method isn't quite as flexible but it works in a pinch, probably faster than trying to do it in Preview. Or combine iPhoto and Preview.