Mostly every person gives some points to saving Sarah with some exceptions (26 and more you get a nice scene with Sarah, but I believe it must be greater than 12 to save her) .
Example: You can save her by making sure to
exchange drinks (crucial step , plus 10 points) and
locking the door when Christian goes to the bathroom. Then just talking to the Carol, Sandra, Charles and Phil on the First Floor (Main Floor).
You can talk to others if you want, as they all contribute to some save points.
Those that don't contribute to any points, if I remember right, are Jason, Markus, Morgan and playing Poker .
The normal version you will miss some scenes, but if you use the
PC Cheat Mod, you can
see all scenes and don't have to worry about Sarah. (Read number 8 in the pc mod features list for information).