This can easily be done with a little bit of CSS/Javascript if you're up for that.
I personally don't like the idea of auto-adapting (assuming that this is different from fluid sites), but I do think that fluid sites are great, and fixed resolution is on its way out.
If you want to get a fluid site started, just go to
http://csseasy.com/ and select "Fluid". They can get you going in no time.