If you just want to take on your husbands surname all you have to do is fill out the DS-19 and send in your marraige cert.
That's true, too. I was actually thinking about my answer to this last night (lost the fight with the 16-year-old for computer time!).
If you want to take your husband's last name and hyphenate it with yours, I think all you have to do is show the marriage certificate and fill out the form the way you want it to appear. Personally, I dropped my maiden name altogether, so my name is First Middle Married. And all I did was show my marriage certificate and tell them that's how I wanted it.
I had to do stat decs for my sons because my husband hasn't actually adopted them legally, but since they had my maiden name, I (and they) wanted them to have my married name.
Anyway, whatever you decide to do, if you need a stat dec to do it, the offer is there!