Comment 34 for bug 270643

2.6.27-11.22 from intrepid proposed fixes the recognition problem for me, on a Dell e6400.

(Temporarily, anyway; there's a bug in the driver that causes the touchpad to occasionally glitch like crazy, sending the pointer wandering around the screen, after which it seems to get re-loaded as a generic mouse and scrolling is broken until you re-load the psmouse module. More about this bug here:
http://www.gossamer-threads.com/lists/linux/kernel/992364?search_string=dell%20e6400;#992364
)