There are two kinds of DVDs, the '+' and the '-'. Diffedrent formats, kind of like VHS and Beta videocassettes. With a Mac, the '-' seems to be the one to use. It sounds like your DVD-R drive is a Pioneer, which is what is on most Macs. Since it is an external drive, you can not use iDVD to burn a disk. Because of licensing problems of some sort, Apple made the program so that it would only work with an internal DVD drive. Roxio's Toast seems to be a good DVDs. I don't use Toast, my drive is internal, so I use iDVD,but all reviews of it that I have seen are good. It's about $99.00. Using iMovie and Toast you should be able to make a DVD that you can view on most any DVD player.
DVD-RW disks are tricky, because some DVD players apparently can't read them. You're probably better off sticking with DVD-Rs. I've heard that OSX has trouble recognizing DVD-RWs, but I'm not sure about that.
Hope this helps.