I recently took advantage of my MSDN subscription and installed Windows 7 RTM on my trusty old Latitude D620 (and for anyone who follows this am still dual booting Server 2008). This installed fine with everything detected and working with the only exception being the touchpad.
To start this by default uses the standard PS/2 mouse driver which is horribly slow to move across the screen. After much searching about I found an Alps driver however although this made the mouse quicker it left the pointing stick enabled. This then drove me crazy as if I slightly touch it by accident when typing quickly the pointer would move across the screen.
Eventually I found a driver from HP that seems to work fine and add the UI to the control panel to disable the pad etc. Check it out at:
ftp://ftp.hp.com/pub/softpaq/sp40501-41000/sp40715.exe
Just trying to make it all work... and then stay that way 