If Djokovic takes one set against Berdych, he's through to the SF no matter what. If Berdych comes through 2-1 and Murray loses, it's Berdych 1st and Djokovic 2nd (two players with same wins = h2h decides). If Berdych comes through 2-1 and Murray wins, then it gets interesting. Djokovic could then only be 2nd to Murray, if Murray wins in two convincing sets against (3 players with same wins = order decided by sets, then games and lastly ATP ranking).
The rules: http://www.atpworldtour.com/Rankings...fications.aspx