The graph shows both candidates in a steady decline, but Coleman seems to be getting hit harder. Barkley (I) is not shown on the graph (although I'm working on it), but it appears that his fiscally conservative position is winning over sour Coleman supporters. Al Franken seems to be running as the generic Democrat, and it appears the tactic is finally paying off.
MN Senate Debate: Live Analysis
The dynamically updating graph for the MN Senate Polls can be found at VoteForAmerica.net along with the other Senate Races and presidential election graphs. The graphs are updated with the addition of each new poll on a daily basis.
If the above link doesn't work try this one.