Microsoft Research Group Shot is very cool. It lets you build a composite photo by merging scenes from multiple photos.
People are cut in half:
Sometimes this just happens (luckily it is only a photo). You can always undo the latest change with the undo button. You can try again by selecting a slightly larger or smaller rectangle to better frame the region you want. This will often work.
Different sized input images:
Images must all be the same size. If images are different sizes or dimensions, you may use tools such as the Microsoft Office Picture Manager and Digital Image Pro to crop or resize images to the same dimension.
Images vary too much:
You will get the best results if all of the images are taken from the same point of view and are of the same group of people. Ideally the photographer will hold the camera fairly still and not change any exposure settings in between shots. Minor view changes are fixed when the images are loaded, the Group Shot tries to align each image.