DVD is 720×480 so your Flash will be as well. Regardless, its best to do your flash project separately. The DVD to Flash option is not a good workflow and often doesnt work correctly
Yeah….I went to high school with Jon and Todd and now they run the largest post house in the area. They bring me on as a freelance DVD/BD author and designer for jobs like yours.
Take a look at this article I wrote for the Cow as it goes over the tools and workflows we will use. Some of my menu design samples as well. Meanwhile, contact me off list.