How can I set an external display (monitor) as the primary one? Currently the MacBook's display works as primary, so every application I open gets open on the 13" and I have to drag it to the 24". I also don't have access to the dock on my 24".

Is is possible to turn off the MacBook screen and use only the one attached via DVI?

(I've just connected my 24" HP LP2475w via Mini DisplayPort to DVI to my MacBook Pro 13", which works great except for this one thing.)
Under your System Preferences > Display, you've got this


Just drag the white bar to the other screen to set it as the main screen.

You might have to do that every time you reboot / reconnect the external screen.