Copying to Data DVD with Toast or itunes works well and is SUPER fast, considering the amount of data moved.
Dual layer DVDs of any quality are usually too expensive, unless a person reqiures the minimum amount of discs used. The DL DVDs are used for uncompressed DVD movie backups.
For archiving music, try to use some better quality DVD media, at least stay away from the ultra cheapo DVD blanks. Then store them out of the light and heat.
Keep an eye on the last date that was burned to DVD, so adding to the library with additional burns is easy to track.
I burned all my ~150GB's of itunes music to DVD, with Toast, but I ran into a glitch and the burn stopped somewhere in the middle of downloading

That made for an organizational nightmare trying to figure out how finish the burning.
Witha growing itunes collection, I decided to get a dedicated external drive just to hold the itunes library.
Having spent a great deal of time importing song files into itunes, it seemed like a backup of the itunes song files was prudent. I never want to have to sit down and feed/listen/edit/label 160GBs of CDs onto my HD again.
I recomend getting an external FIREWIRE Hard Drive or combo. Doesn't sound like you need that much room and HD prices are very inexpensive, considering the ease and safety in backing up ALL your stuff, not just itunes!
Create a few partitions. Especially make a partion to hold a complete "clean" copy of your OS and personal files. SuperDuper is a good backup software, but took a while to learn.
If your thinking that backing up seems like a smart idea, and it ALWAYS is, it's not much more difficult to set up a back up of everything, at the same time.
I'm so glad I backed up (cloned) everything to an external drive! 2 days I somehow goofed up safari and couldn't be fixed after much effort. I booted from the backup external firewire drive in minutes, using it exactly like the original drive and then used Super Duper to to a complete replacement of contents to the main HD. Suspected conflicts from recent downloaded apps.
Problems fixed, with a few key strokes. I will NEVER go without a cloned drive again! Turns a potential gigantic trauma/hassle caused by a drive failure or software meltdown into a non event.
The G4 and an external drive, when retired, will likely wind up becoming a music server, integrated with a home stereo system.
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Dave