well I know Intel makes processors with built in hd graphic what socket is a t400 and do they make processors with graphics for it.
More aboutt400 upgrading graphic solution
Lenovo t400? No can do, it's soldered to the mobo. Most laptops tend to be except for a few $1200+ laptops. Also it seems it's around 5 years old so really shouldn't even be thinking about upgrading it.