According to Troy Johnson, Smashing Pumpkins and White Stripes are both definitely not playing Street Scene 2007. I'd take his word for it. White Stripes will be at Vijas Concerts at Bayside on September 18, according to their website. Cold War Kids are still listed on their site as playing Street Scene, which is a little odd to me, but whatever.
I don't go to Street Scene for the headliners and don't get any feeling about these two particular bands, so I'm just anxious to see who really is playing. Just stretching my guesses and looking at Tour dates, I'd be happy to see Arcade Fire, Kaiser Chiefs and Spoon among a ton of other "wish list" bands.