This is kind of a weird poll, courtesy of SurveyUSA. Kerry is generally ahead in Iowa, which is nice. But apparently, Gov. Vilsack doesn't provide the boost in the state one might've expected.
SUSA. 5/24-26. MoE 3.6%. (No trend lines.)
Kerry 48
Bush 45
Other 8
Bush/Cheney 48
Kerry/Vilsack 45
Other 7
Usually, people respond to having one of their locals on the ticket, but if SUSA is to be believed, Iowans don't want to share their governor with the rest of the country.
SUSA notes that the fluctuation is within the margin of error, so one cannot conclude that "Vilsack hurts Kerry". However, the converse cannot be said either -- "Vilsack helps Kerry".
Regardless, you better believe that Kerry is polling the crap out of any potential veep, running focus groups, dial groups, and conducting the most intrusive background checks anybody will ever experience.