[tonyvdb]

Have a look here at the Dolby website. They have a diagram showing where the speakers should be placed for 5.1 or 7.1 speaker setups.

 

[tonyvdb]

If you use BluRay alot for movie watching there are more and more movies that have discrete 7.1 mixes there is a difference, however 5.1 is still the norem for all standard DVDs and that really makes little difference in a small to medium sized room.