Sharing a layout real quick I made for ScraPerfect. It's hard to believe it was just over a year ago we were strolling around London doing my best to fill up my camera's SD card. I gathered several of my favorite shots from our first stop and combined them into one big block to print.
To create this photo block I made a new letter-sized document in Photoshop. I created a custom crop at 300 dpi and used it for each photo, dragging it onto my new document after cropping. When I had all six lined up and spaced I realized the photo block was too big. To remedy that I selected all six layers, held down my shift key and dragged the lower corner to resize everything together.
Holding down the shift is important -- it keeps the proportions the same. Otherwise you'll end up with wonky, distorted photos.