I have to second the 7.1 setup. If you're doing a dedicated HT room...by all means do the 7.1. At the very least 6.1 because there are movies that are out now that utilize 6.1 discrete such as Lord of the Rings and Gladiator.
And there are several more that utilize Dolby Digital EX, which does it's own matrixing job for 6.1 and 7.1 speaker setups. There's even more of these types of movies such as Finding Nemo, Toy Story 2, All the Star Wars movies on DVD as well as several others. So, again, if this is a room dedicated to home theater, don't sell yourself short by not getting all out of the encoded surround sound that you can. If you can afford the extra speakers, do it. There's reasons to go that route.
Live it up, enjoy the sound!
"We're on the island of Misfit Toys"