Macbook Pro with external display

Hey, I've been looking for a concrete answer to my question but various searches only serve to confuse me more. I was going to ask this about an hour ago but got distracted by the big Steam on Mac story - very exciting! So here goes:

I own a 22" monitor with a DVI input. I am planning on buying a Macbook Pro 15" (after the refresh if it ever happens but using the current model as the example for now) and I want to use my monitor as a second display.
I need to know how this works (ie set-up in OSX) and what options are available.

1) Is the picture just a mirror image? If so, what impact does the difference in aspect ratio have? Does it just stretch things out to the size of the monitor or does it use the monitor's full resolution as well as size?- this applies to the following question also.
2) Can you use the display as an extension to the workspace on the laptop? If so can you set up which side the external display is on? Can you switch between mirror and extension?
3) Can you close the Macbook and carry on working on the external display? If so how does the change-over occur - i.e do all your windows stay with the book or do they all move over to the external? And what about mouse and keyboard?
4) On a similar note and with the above questions in mind, can you really connect the Macbook Pro to the new 21.5" iMacs?

Thanks a lot if someone can clarify this for me!

 

That's great, thank you for your help!