The 4500MHD, like the majority of integrated laptop cards these days, is actually pretty decent. Core Duo 2 GHz and 4GB ram is fine for playing maps of any size, although you WILL get longer wait times in between turns later in the game for Large and Huge maps. 2Ghz laptop != 2Ghz desktop in the majority of circumstances, unfortunately.
You can put all the graphics settings on high if you like, it'll run smooth as butter in the beginning. By 1500AD you'll notice some drop in framerate, but it's still playable. Mainly the issue is scrolling around gets a little jumpy, and the wait between turns.
For optimal graphics, I'd recommend turning "Multisamples" off (from 2 -> 0 in the civ4 graphics menu), and instead turning on anisotropic filtering 2x from your graphics card settings menu. It makes for a smaller framerate hit (~5% versus 15-25% for the multisampling), and makes the textures MUCH sharper. Multisampling is nice if you have a solid graphics card, but for integrated laptop graphics Aniso is where it's at.
