Just some tips from a sorta local-- While downtown is the most central, it is also the most expensive, and trafficky too. Try and stay on the WEST side if possible, it makes the most sense. Ask when you book your room if they are in the west side- most chain hotels have locations at both. I am a big fan of the Hampton Inn, in fact, I'll be staying there June 5. They usually have decent breakfasts (cereal fruit, bagels, juice, and some hot food which usually looks nasty to me) and it's in a pretty good location.
Anything you may need, be it bike stuff, nutrition can be found anywhere- it is a very tri friendly kind of city, I recommend Fleet Feet in Middleton for everything but bikes, and depending on where you are staying, there are multiple mechanics and bike shops all over.
There is also a specific Tri Shop called Endurance House in Middleton (where there are LOTS of hotels too, btw, it is the town just west of Madison and is practically a part of Madison) It is owned by a multi time Ironman, and he has always been really nice and helpful and interested in supporting the community. You guys would love him.
Food and Beer. The real reason for the wknd, right? 
If I can be helpful scoping out good spots for mass meetups/meals I am happy to do so. The Great Dane in Fitchburg is big and would accomodate a group. It is a traditional WI brew pub. Tutto Pasta has a large variety of pasta (every triathletes fave meal) and enormous portions.
I will be available off and on all weekend for support, SAG etc. I do have a few responsibilities (like, uh, closing on a house and moving! oh and horrible inlaws I would love any excuse to escape, like, uh, "my BT friend needs me to drive a tube out to him!"
but I can be "on call" if y'all need someone.
I am so excited, IM makes me so happy, after IMAZ yesterday, I can;t wait to get back to MSN ands see all the zillions of people who come through to train.
-Hollis