How do I make 'graphical' DMGs?

The best example of a 'graphical' DMG that I have seen is the Firefox DMG. There is a background, and the icon is positioned in a certain place.

I know how to make regular DMGs, but can I spruce them up to funkiness like that?

You just give it a background like you would any normal folder.

Go to a folder.

Set it to Icon View.

View > Show View Options

Under "Background:", select "Picture"

You know the rest. ;p


edit:

By the way, in order to include the background picture in the Volume (the DMG once it's mounted),
this is what the Firefox Volume does:

It has a hidden folder called ".background" (The dot at the beginning makes it hidden.)

Inside is a picture named "background.png", which is what you see as the background of the Volume.