If you just want to keep it simple, put one "SpawnTeam" (from misc) entity at each starting point and give each spawn entity a different team where is says "desiredTeam" in the edit entity info box. When people pick the specific teams, they will spawn at the corresponding spawn points. If the teams are not hostile to each other, then go to the levels tag, then to team, and set up all the boxes at -10.
Hope it all works.