I have a Dell Inspiron 4000 with an ATI Rage 128 Mobility. This works great, and I've been running nothing but Debian for more than a year now (Mandrake and WinMe before that). Everything works: modem, network card, pcmcia, 3d acceleration from the ATI (the little it has). In short PERFECT. Now, my dad got a newer Dell laptop and looking at all the cheap SiS crap in there I don't think anything would work with Linux.
As for the newer ATI cards, they'll surely work to display 2d graphics, but whether you'll get 3d graphics is another story. Or it may work (most likely the case), just slower than it should.
Good luck.
