I guess you'll have to split your projects in different parts.
1 is the lock on the door
2 the way people have to enter their codes/passwords. (keyboard, wireless ?)
3 perhaps some sort of display to show 'm what their doing
4 getting each part to work individually
5 combining them together
One could think of more things like triggering an alarm, different codes for different people to know who's in or... opening the hatch below the burglar after 3 mistakes.
Knowing enough about programming and electronics to finish a project like this is a must.
Unfortunately you haven't told us whether you already know a bit about programming and electronics/micro-controllers.
If not it's probably best to start with simple electronics/programming.
Once you know that it's a lot easier to start combining the different pieces of your project.http://arduino.cc/en/Tutorial/HomePage