If I buy the 16:9 Anamorphic Adaptor for the AG-DVX100A, what would I do in editing to make sure that the image doesn't end up being stretched vertically on a regular TV (ie how do I add the black bars and resize the image so it's widescreen without losing quality)? Anybody know? I'm using Premiere Pro. Thanks for any help.

Create a Widescreen Project. And resize the image to fit the window. Thsi will create your high res widescreen master. please refer to: Exporting Widescreen in Premiere to learn how to make your letterboxed 4:3 master.

It is always better to work in the highest quality possible, then put your video into letterboxing. Therefore if you get into a festival that accepts WS DigiBeta you can get a widescreen master done from your hi res 16:9 master.