The Milwaukee Bucks swapped first round positions with the Houston Rockets and acquired 7 foot center Samuel Dalembert in a trade one day before tonight's NBA draft.   The Bucks gave Houston it's 12th overall pick in the first round along with three backup players, former Wisconsin Badger forward Jon Leuer, forward Jon Brockman and guard Shaun Livingston.   In return, the Bucks get Dalembert, Houston's 14th choice in the first round, a future second round pick and cash.  General Manager John Hammond is likely going to add more size to the roster to team with the veteran backcourt tandem of Brandon Jennings and Monta Ellis.  Milwaukee also has a second round pick, the 42nd overall choice.