From what I understand, Iowa doesn't really have one set team that the fans despise. It really depends of what part of the state you're from. People in northern Iowa hate Minnesota, people in central Iowa hate Iowa State, People in the Quad Cities hate Illinois, and I suppose people from the Dubuque area don't like Wisconsin although I don't really know. This is based a lot off of message board reading though as I don't know many Hawkeye fans outside of Iowa City and the Quad Cities as those are the only two places I've lived. I think there is a pretty good rivalry between Wisconin and Iowa because they seem to be two similar school at this point (two middle of the pack, non-OSU, Mich, or PSU, Big Ten teams who have battled for the conference on occasion lately, and they also have seemed to be the best middle of the back teams) but I wouldn't say there is a lot of venom between the two.