It will the house or both (or neither if the rats hang on to the house). The Senate is unlikely. It would take more a perfect storm of the right candidates running and a landslide on a level that would guarantee the GOP was also taking the house easily.
I think the House is a good possibility. In the Senate, Republicans would need to knock some northern senators such as Dodd and Specter, as well as Blanche Lincoln and Harry Reid, and several others. If can get back up close to 50 Republicans, that should also enable them to end Obama’s agenda and keep things static until 2012 when they should pick up more seats in the Senate.