Disk Utility Help and DVD Help

Hey guys,
2 questions i think..

1. A long time ago when i first got my powerbook, i was looking for a way to protect my files by password, i created a disk image stored in my documents, password protected and made it 5gigs. I realize i no longer nead that much space and want to either a.) delete the disk image, or b.) reduce the size.. how do i go about doing this?

2. I want to back up some data, documents, home movies, spreadsheets, etc. on a DVD-R, but i want it to be password protected, any way to do this? Either i want it so that when you pop in the cd, it asks for a password, or when you open the cd, to access certain folders it asks for a password?

Sorry for the lenghty questions, btw i am on the 1.5ghz Powerbook.

Thank You,
i4k20c.

 

Anyone?
Let me rephrase. I found out after creating a new image just on my hardrive, if i throw it away, it is fine. The 8gigs will free up again.

But what about the DVD-R Question? Can i just create the DVD-R image, the one that is 4.7 gig, and drag the .dmg to the dvd and burn it? Do i have to mount anything, can i even do this? Please...?