It all depends of course on the length of the production but, depending on what encoding software you are using, you can set a bit rate which will use more of the disc and at the same time give you a better quality DVD.
How long is the video? At full quality (about 8Mbps for video encode), a disc will hold 60 minutes of video, so if you have like 20 or 30 minutes, then the 2GB makes sense, and you can NOT fill the DVD. You will have the option of using uncompressed audio rather than Dolby AC-3, since you have room to spare.
Jeff, don't you think that 8mbps is a bit too high if you want to be absolutely certain that the DVD will play in all players? That's often the reason for problems in playing. I find that 6.5 to 7 is safer and won't make any appreciable difference to the quality. Using this setting as an average with a double pass encode gives very good results with BitVice as the encoder.
Funny that you should mention the high data rate, because I usually tell everyone the exact same thing! I'm seeing more and more posts suggesting that playback issues don't exist with high rates...but I've always figured better safe than sorry, so why push it? I also typically choose CBR over VBR, but that's another argument.
I only mentioned the 8Mbps rate to help illustrate why his disc is not filled to capacity, and was not suggesting that is the best choice to encode at, but I should have added that disclaimer. The majority of programs that I produce are 90-120 minutes or even more, so I often encode at 4.5 (or less) and have never ever had a customer complaint about the DVD quality.