ATI GNU/Linux driver support for Mobility Radeon

Does the ATI GNU/Linux driver support Mobility Radeons? Cos i'm buying a laptop soon and i don't want to spend money on a good graphic card only to find out that there aren't any drivers for it.

You will have to look at what specific video card is in the laptop and compare the support for it here, as well as here.

You could test the laptop by booting a SimplyMEPIS disc,
or find the display adapter name in the XFree 4.x column of this list:
http://www.linux.com/howtos/Hardware-HOWTO/video.shtml