How do I do this?

Someone ured me that it's not too hard, but they neglected to tell me how it's done. I'm trying to create a countdown ticker that people where people can input their impending date and can add it to their websites, blogs, etc., just for the heck of it. I have all the graphics done and stuff for the background... Now I'm just stumped on a couple of things. What's my next step? How do I actually have the little "form" they fill out on the website put their time on the graphic that will refresh every day? Any help would be greatly appreciated! Thanks!