Creating Disk Image of MacBook to External Drive

My MacBook has to be shipped into Apple for various weird things.

I have a Time Capsule back-up, but I'd like to clone the disk as well to another external hard disk before I send it in.

My Time Capsule was so hard to set up (read days and days of AppleCare phone support) and it makes such a loud noise when it's writing data that I just don't trust it as my sole back up.

What I used to do was start with a fresh external hard disk and use Super Duper to clone the computer's disk.

Now the thing is, I do have an external hard disk with plenty of room, but it's got movies and stuff saved on it. So, I figured cloning the MacBook to the disk with files already on it is going to cause problems.

Then it occurred to me that I could use Disk Utility to create a disk image of my MacBook's HDD and have that image saved to the external hard disk!

Three questions:
1) Is this possible?
2) If for some reason I need to recover from the disk image file, will I be able to?
3) If yes to 1 and 2, should I do this while booted to a Leopard DVD rather than while running the hard disk I am cloning? I'm assuming I should run from the DVD, but just checking.

Thanks!