A laptop version of the ATI 5xxx series you mean? I'm not sure if it will be available anytime soon... ATI will have to work through 4xxx series I think, and they might come up with a different naming convention in the future.
lol, ATI's already launched the mobility 5 series: http://www.tomshardware.com/forum/56103-35-official-5000-specs
tntomek: I can't honestly say when or if they will adopt them. Dell seems to be somewhat slow in adopting newer graphics cards for their laptops. It seemed to take them a while to move on from the mobility 3 series to the 4 series. Engadget usually has some sort of news about changes like this, but I have yet to see anything. I can't imagine that it will be too long before they move on to the 5 series, but maybe they are waiting on NVidia. If I see anything new, I will post back.