An error occurred while burning the disc.

I tried to burn some stuff onto a DVD today with my PowerBook. Here's the info on the burner:

MATSHITA DVD-R UJ-845E:

Manufacturer: MATSHITA
Model: MATSHITA DVD-R UJ-845E
Revision: DMP2
Serial Number:
Drive Type: CD-RW/DVD-RW
Disc Burning: Apple Supported/Shipped
Removable Media: Yes
Detachable Drive: No

I bought some DVD's on sale at Radio Shack, and when I tried to burn a movie and a few photos onto a disc, the progress bar showed it starting to burn, then it stopped and I got this message:

"An error occurred while burning the disc. This disc cannot be used."

A little research here at the Apple forum brought me to this site:

http://www.digitalfaq.com/media/dvdmedia.htm

And after downloading a little program called DVD Media Inspector, I was able to classify the DVD's I had bought as:

"4TH CLASS MEDIA:
Pathetic garbage media, landfill material, about 0-50% success rate...."

OK, off to Mega Lo Mart, where I bought some nice, expensive Maxell DVD's.

Media Inspector doesn't see my fancy new DVD's. When I try to burn stuff using the Finder, I get the same result as before.

Getting desperate at that point, I located and downloaded updated firmware for my model of Matshita superdrive. I'm not sure what firmware is, and there was a free range one and a standard one, so I went for the standard one. There were dire warnings in the readme file about "flashing" a superdrive being on the same risk level as open heart surgery. I flashed my superdrive. (You can say that here, and it's not dirty.)

I also tried burning using iDVD, and after much preparation, it started to burn, then spit out the DVD. I tried three of the landfill DVD's and two of the Maxell ones. I'm out of things to try. Any ideas?

I have never tried burning DVD's before. Am I doing something wrong?