Version 3.0 Prototype Started

Fortunately, all I want is a GUI rewrite. You see, my company maintains three web sites: the yackety-yak blog site (here), the shameless commerce site, and the production code. For the last couple of months, I've been kicking around an idea in my head: what if we used the same style sheet for all of them? Not only would they have the same look-and-feel, but I could theoretically update the master style sheet and badda-boom, badda-bing, the whole shebang changes. (Don't you love it when somebody says 'theoretically'? Theoretically, my grandmother is a trolly car)
Constraining this even further, I'd like no more than a 50K download with no round-tripping: that is, I want everything possible to happen right there on the client. I'd also like to win the lottery and be an astronaut.
I'm still using .NET, and the business layer of the program, so none of that should change -- the design is solid enough not to need any fixing. This will be strictly UI. A couple open questions remain: should I use custom server controls for div contents? If so, should I encapsulate the javascript inside the controls? If I do this, I should end up with some completely new way of writing web applications. It also leads to some interesting construction paradigms. For instance, I could imagine slapping the thing out using the biggest whiz-bang .NET controls possible, then following up with the thin, fast version. This gives the user quick functionality while letting you "build one to throw away". I'll let you know how it goes.