It may be worth tracking down the last version of BootCamp to support Vista and see if the included touchpad drivers work. You might be able to do it with this tool. I believe the 3.x series is the last to support Vista. I don't have full confirmation of this but I believe the Early 2009 to Late 2011 MBPs use the same touchpad so in theory, a driver from one of the plethora of BootCamp versions for those models should work.
Apple's BootCamp software is a mess. I don't know how helpful this is, but I know that running older versions of BootCamp on newer versions of Windows can be done easily using compatibility mode so I don't think the OS checker is that restrictive.
