Responsive design, that is the word your looking for. It is becoming very popular now, and it looks like that very very soon without responsive design you wont be able to do anything, as more than half of internet traffic is comming now from other devices but PC.
There is many different articles about responsive design, as well I have seen few good ones on sitepoint. Plus on google you will find many tutorials on this theme.
Main idea of Responsive design is that all properties is set to fluid width, such as em's or percentages. So depending on screen size, your website will resize, will adapt.