Just to add my $0.52: it should work fine, since I know that the game is playable on much less.
It's not going to be a stellar performer, but it should get you through most mods without too much trouble. A lot of the game engine is still memory and CPU bound, not GPU bound. Most of the memory issues, and some of the CPU issues, are going to be solved with 3.6.10 and later versions. ATI has always had issues with OpenGL apps, and the performance from them usually suffers, but that's a driver issue and not really anything hardware related. Now that AMD is involved though, I expect that we'll see some better driver developement in the OpenGL area.
If you use up-to-date drivers, avoid using AA except at low resolutions, and fiddle with your detail settings a little bit (lowering "3D Hardware Textures" will save you some video memory), then it should play pretty well for you. But as WMCoolmon said already, just be sure that you always play the game with the laptop plugged in, since the power saving features will kill your performance otherwise.