A user called "Smucker" over at the Steam forums discovered that if you changed a couple of bytes in the exe, the game would run on Windows Vista with out crashing. However, to make the edits, you would need to use a hex editor and potentially screw up your exe in the process. To make things easier, I have created a simple little tool in VB that will do the edits for you. Just download the patcher, put it into your manhunt folder, and run the program. At the current time, only the Steam version of Manhunt has been tested. It is most likely that the patcher will work with other versions. If you have a version of Manhunt other than Steam and the patcher works, please contact me at aj@rockstarwatch.net.

Official Site: Manhunt on Windows Vista Patcher