I found a workaround of sorts to make a backup DVD (on a PC at least):
1)Put in your last backup DVD to find out when you made it.
2)In iTunes under "Store", select the "purchased" list.
3)Sort your purchased list by date added.
4)Select all the items you've purchased since your last backup (easily done by first selecting the first item you purchased since your last backup, then going to the top of your list and selecting the most recent purchase you've made while holding down the shift key).
5)Select "file", then select "new playlist from selection", then name it.
6) Put blank DVD in drive.
7)Right-click on the playlist you created and select "burn playlist to disc".
8)Select "Data CD or DVD" and then click "Burn".
...and voilà!, you should have a backup disc.
(I realize that this description is rather in depth, but I've worked tech support before and realize that some people will most definitely need it to be that way.)