so I installed windows 7 using the bootcamp assistant on Mac OS X, everything went fine, but it automatically always boots into Windows 7? I don't even have the option to choose which OS? why is that?
Did you try holding the Option ⌥ key while starting up your computer?
If you're able to start the startup manager that way, you may be able to set the default start-up volume by pressing ctrl while clicking on an arrow under the volume of your choice (depending on your model).
As has already been mentioned, you can hold down the Option key immediately after turning on the computer to get the boot manager. apple.com
You can also select the default OS (automatically boot to OS X instead, for instance) in a couple of places.
In OS X, open System Preferences and select Startup Disk. Then click on the OS you want to be the default.
In Windows 7, there is a similar option in the Boot Camp software that should be accessible down in your System Tray. If you haven't installed the Boot Camp drivers yet, you should. They make life a million times better while using Windows on a Mac.