ok, I didn't do the pictures myself, I just combined them.
I have Photoshop 5.5 too. I freehanded around the girl using grey to get rid of the background she was on. To do this with any sort of accuracy, you need to zoom in at least 300%. Once I did that, I found the background picture I wanted.
Open up both pictures, drag the picture of the girl onto the background and position it. Choose Layer Options, hard light and adjust the percentage until you are happy with it. Experiment with some of the options to see what they can do. You can re-postion the pictures at any time.
This is just one of many many many things you can do with Photoshop. The way I learnt was to just muck about with it one day discovering what everything does. You do need patience though, especially when freehanding around pictures. The big key to doing anything productive in photoshop is using layers. Just drag and drop as many layers as you like and you can have a different effect with each layer. You just have to experiment until you find the right combination.