Laser Security

Hello, I just registered for the forum. I am a student of telecommunications and I have to do a project. My idea is to use arduino. I'm pretty lost and I hope someone can help me out. I have a arduino Diecimila and a laser. I've cleared, but the problem is not as connected to the board. I also like to know which receiver I have to put, I thought of a LDR, but not that kind. I would be grateful if someone could help me out. Greetings to all.

Perhaps you could give some clear idea of what it is you're trying to achieve...

A Laser tripwire i'd guess im not a fan of LDR's, a photo transistor is more usefull i think as it gives a clear yes/no result

Perhaps this is what you are trying to achieve?