Ive made an interior where there is one room that i'd like the player only get access in to once he has completed a quest. In other words I'd like the door locked and inaccessible until the player has completed a starter quest. I am not sure which scripts to use or if it is even possible. I could have the door locked and create a key which is given to the player upon quest completetion but it would be a little wierd considering there is already a person in the room which gives a new quest.

You could probably use the BlockActivation() function for this. Once the quest has reached the right point, you could run BlockActivation(False) on the door. All of this would be done in a quest stage's Papyrus script fragment.