You can do that with photoshop - but Arcsoft has Trials including the Collage Creator you can use before you buy - I've never tried them but Arcsoft is a good name
http://www.arcsoft.com/support/downl...load_trial.asp
also Googles Picasa is a good photo program and totally free - it finds ALL the pictures you have in your computer automatically - which is pretty cool - but I don't konw if it will do what you want
http://picasa.google.com/