To install templates:
1. Select the Print panel in Lightroom-3:
2. In the left panel point the mouse to the “User Templates”
right-click and select “Import”:
3. In the pop-up window select all the templates you want to install ( they all have .lrtemplate ending on the files). Click OK.
4. Templates should appear in the left side panel under “User Templates”
To place pictures to the template, just drag and drop photo to the place.
To export and save a template in Lightroom 3:
1. In the right-side panel open up Print Job and make sure that Print to is selected with JPEG File:
Then press “Print to File” button and Save a collage:
That’s it! You are done!
Now if you want you can open a JPEG file in Photoshop (or Lightroom) and resize it, or if you want to print it, just load it to your photo-lab account.
*** UPDATE ***
Video tutorial to demonstrate how to install and use Templates for Lightroom 3: