hi john.
i my self don't know too much about the seed.i always bring the tubers in and store them over the winter.and then plant them in the spring after frost is gone. hopefully some one else might be able to help. i'm a newbie to the web also.
happy growing joan

here's a link that might helphttp://images.google.com/imgres?imgurl=http://www.bbc.co.uk/gardening/images/competition/300x193_dahlia.jpg&imgrefurl=http://www.bbc.co.uk/gardening/competitions/dahlia.shtml&h=193&w=300&sz=10&tbnid=mPKlyZnGD2eomM:&tbnh=71&tbnw=111&hl=en&start=1&prev=/images%3Fq%3Dpicture%2Bof%2Bdahlia%2Bseed%26svnum%3D10%26hl%3Den%26lr%3D%26client%3Dfirefox-a%26sa%3DN

You won't get the same dahlia from seed as you grew from tubers. The only way to get the same dahlia is to keep the tubers. The dahlia has too many gene combinations to come true from seed.
If you want to see what a dahlia seed looks like go to our "Seedlings" Album at this site. It also shows the pods & how we open them to get the seeds.

Here is a link that might be useful: Wynne's Seedling Album