In the event that teams finish with the same record, each tied team receives the average of the total number of combinations for the positions that they occupy. In 2007, the Minnesota Timberwolves and the Portland Trail Blazers tied for the sixth worst record. The average of the 6th and 7th positions in the lottery was taken, resulting in each team getting 53 combinations (the average of 63 and 43). Should the average number not be an integer, a coin flip is then used to determine which team or teams receive the extra combination(s). The result of the coin flip is also used to determine who receives the earlier pick in the event that neither of the tied teams wins one of the first three picks via the lottery.

http://en.wikipedia.org/wiki/NBA_draft_lottery