What with people chatting about Avalon's NineGridBrush, and then today a request for the effect on a webapplication I manage, I've been thinking about how one could make this with a simple web control... I've come to the conclusion that, with v1 of asp.net, while it's technically possible to get runtime execution working via jumping thru a few hoops, the designtime experience that you want, just isn't really possible.
However, with Whidbey, this control would definitely be doable. For runtime, it's all about the DynamicImage control. Take the single image that the developer specifies, and dynamicly chop it up into 9 bitesize pieces. At design time, it's about combining great new control designer features like editable, clickable regions and GDI drawing.
My mind races when I think about cool stuff like this.