The idea of delaying the seating of Senator Brown came from Rush making wild accusations in an attempt to discredit the Democratic party. It was never going to happen, except maybe in Rush's paranoid brain. Drug addiction does that to people.
Actually it came from the democrats themselves, that is if you trust NBC:
http://www.msnbc.msn.com/id/34952671/ns/politics-more_politics/
"Brown will finish Kennedy's unexpired term, facing re-election in 2012. Senate Majority Leader Harry Reid pledged to seat Brown immediately, a hasty retreat from pre-election Democratic threats to delay his inauguration until after the health bill passed."