MidAmeriCon II will be occupying the southern part of Bartle Hall and the Convention Center (which is the area bordered by Central Ave and Broadway Blvd between 14th and 16th streets). The easiest way to reach Registration is to enter from the street level 2200 lobby at 13th St and Central Ave and walk indoors down the hallway to the 2300 Lobby (there will be signs pointing the way).
Additionally, there is an entrance from the city garage connection to some of the hotels, Aladdin and both Marriotts, that accesses through the Auditorium or below the 2200 lobby.
Registration area detail from above map:
Grand Ballroom/2501 (AKA Pat Cadigan Theater) for Hugo Awards and Masquerade.
Also the Great Hall/3501 (AKA Tucker Stage) for other events:
The Exhibit Hall (up the escalators from Registration):