The 6600GT is about as fast as the 9800Pro, but unline the 9800 the 6600GT supports shader model 3.0 while the 9800 is limited to 2.0 thus not allowing you to play newer games that require at least shader model 3.0. The 2400XT is a dog and even though it is a DX10 card, it's too slow to play any game in DX10 and is still slower than the 6600GT in DX9
Performance-wise, I'd disagree with the listing linked; it tends to usually perform worse, across the entire board, than either the 6600GT or 9800pro. Howeve, it shouldn't be by a BIG margin... If you're fine gaming with the discrete cards mentioned, the mobility one won't be that much of a disappointment. Just know that you'll only be able to use small resolutions with the card, which might not equal the laptop's native resolution.