You may find the answer here:
http://en.wikipedia.org/wiki/NBA_Playoffs
Seeding Criteria
Tied Teams
In the event that two teams end up tied for the same seed, the following tiebreakers are employed[4]:
1. Head-to-head
2. Division record (if the teams are in the same division)
3. Conference record
4. Record vs. Playoff teams, own conference
5. Record vs. Playoff teams, other conference
6. Net points, all games
Here is another link:
http://www.nba.com/features/seedingprimer07.html
"The top four seeds will be the three division winners plus the team with the next best record. Those four will be ordered by record (and tiebreakers if needed), so it's possible that two teams in the same division could hold the top two spots, with the other two division winners at Nos. 3 and 4.
Seeds 5 through 8 are the next four teams according to record (and tiebreakers if needed)."