T40: Original Banias system. First generation Centrino.
T41: T40 + anti-shock hdd mounting thingie. I think it also added PC2700 support. Added 802.11G. Fixed motherboard & cooling issue for most part
T42: T41 with Dothan Support. Better videocards available (9600), added 15" to lineup.
T43: Sonoma chipset. 533mhz Dothan support, uses DDR2, PCI-Express based. Louder, less battery life, but fastest.