How to set spawn protection in Minecraft?

I just created a minecraft server using the minecraft_server.1.7.4.exe file on Minecraft's website.

It works and I'm OP.

I have created this server just for me and my friends and obviously they are looking to play pranks or grief it. I don't mind but I want my spawn kept safe.

I haven't created it using Bukkit and just want a spawn point protection so only I can make edits (build and destroy). I don't want any of my friends griefing it.

How?

Any links or clear instructions will get 10 points.

A part around your spawn is always protected, so nobody can place/breake blocks there if they are not op, its just a little part tho.

Get a bed for everyone. Then sleep in it. You will spawn in your bed. If your friends mess with your bed them you still have the real span area. Find it with a compass and build a wall around it. No roof. If you want you can put a chest for emergency supplies there if you get killed. You can also have two beds so you will spawn in the most recently slept in bed. If that gets destroyed then you will spawn in the second bed. Make sure to sleep in the beds. Hope you good luck!