Now that the Kinect is more than a month old, it may be worth looking at more closely. Your daughter is 6-7, there are gobs of Nintendo Wi games to be had, and still just a handful of MS games worthy of your short stuff. Seriously though, My 6 yr old loves to sing and dance. Even without Kinect, the xbox has Lips and Rockband.
I am a gamer, if you game at all, the xbox is for you. If you watch bluray it is a no brainer get the PS3. Which also has a singing game and Rockband.
If you are not a gamer at all....wait until the next generation and spend non-digital time with your young one. Put on an album and play UNO. When the weather warms up...play some kind of ball game.
Teach her the fundamentals of reading, and the enjoyment of the story... so she can really immerse herself into the next gen of role-playing games.