Some bus lines are free on New Year's Eve. The bus company is really helpful when you need to get around on teh bus. Give them a call and tell them where you are, where you're going, and at what time, and they will tell you how to get there fastest by bus. Calling the BusLine at (414) 344-6711 is a great way to get the route, schedule and fare information you need.
If you'll need a taxi for the night from somewhere, find a couple of company phone numbers beforehand. I think Yellow Cab and American Taxi are the big two in Milwaukee. You may see a taxi on the streets when you need one, but odds are you will not. Major hotels will if course offer easy access, but this isn't Chicago or NYC. Plan ahead.
A car remains the easiest way to get around Milwaukee. The city is fairly logically laid out, and traffic is minimal compared to major cities. If you're not accustomed to driving in snow and ice, avoid visiting in the winter months.
Milwaukee's airport has been interestingly refurbished, and is well appointed and easy to navigate. Although your choice of flights will be more varied if you opt to fly into Chicago's O'Hare, app. 90 miles South, this airport is much more traveler friendly. Normally not overly crowded either. One of my favorite things about this airport is that you can access rental cars directly from the terminal without requiring a shuttle bus. Also has good shopping areas with local flavor.
Get I94 from Chicago and drive north. Or take an airplane to the Milwaukee International Airport. I suppose a trip with a ship is also possible through the lake Michigan, but unfortunately I don't have any information about it.
Coming from Chicago, the easiest and fastest way is I-94 North. Also the Amtrak train is quite comfortable. If you're driving, watch out for highway patrol. Apparently Wisconsinese (?) take speed limits very seriously.
I highly recommend driving to Milwaukee on I-794. The highway is near the lake and has a long bridge with an excellent view over the city.
The city itself is quite accessible by foot, as long as you have a good grip to the pavement (heavy winds, reminiscent of Chicago). Milwaukee has a public transportation system also.
I went form Chigago and got the Amtrack to Milwaukee.
I found that driving was the easiest way to get around