I see there a several ext CD burners for sale.
Just thought I'd mention you can pick one of these up and swap out the CD burner for a DVD burner. Although iDVD wont work DVDSP and Toast will both work.
I've done just this with a DVD-RAM drive which I use for daily backup.
Just a cheap suggestion.
2.6 i7 MM, 27iMac i5
1.4 MBA 11"