Prefix in New Thread - How can I do this?

[ColorsDeluxe]

I'm developing a vb forum, and want to add a feature.
When I create a thread, I want to add a Prefix for the thread.

You can see a demo here :

http://images.blue-deluxe.com/upload/screenshot.png

Think on domain forums, like in the screenshot, when somebody write his domain as a thread name, he could choose from that dropdown, the extension .com, .net, etc.


Later Edit :

Also, how I can make the links, SEO friendly?
forumdisplay.php?f=107 - this thing to appear as the thread name, or something similar.
How can I do this?

Thanks.