Macbook Pro with OSX and Windows - How to set default boot partition?

I have a MBP with OSX 10.5.7 and Windows 7 RC installed (created the partition with bootcamp, then installed 7 manually).

When I boot, I can hold down the option key to select which partition I want to boot. But if I forget, it always boots into Windows.

Is there a way to change the default partition to boot OSX instead of Windows by default?

 

Thanks - works perfectly!