The Vikings would be dumb to do this. Sage Rosenfels IS their man, and it should stay this way.
He has a career 81 QB Rating, as a backup, meaning he was thrust into his role, and was not prepared, the most games he has ever played in his career in one season is 9, he also has been with the Texans and Dolphins his whole career, two teams that until last year, were for the most part bottom feeders on the NFL (Dolphins were not as bad as the 1-15 they posted 2 season ago, but still did not have the potential the Vikings have)
The Vikings have SO much young talent on offense, they need to establish this, and not fuck around by bringing in Favre for a year, they need someone who can be their QB for 3+ years at LEAST, because they have a solid O-line, and the best young offense in the NFL besides their QB position (Peterson, Rice, Berrian, and newly drafted Harvin). Bringing in someone like Favre who IMO is equal to Rosenfels in talent, who would want a nice sum of money for 1 year, and who could only contribute for 1 (MAX of 2 years) just makes no sense.
The Vikings have so much potential, and like I said earlier, I think in 2 years they could have the best offense in the NFL.