Which Lexmark AIO model do you have? If can't find the Vista compatible driver on the Lexmark website (support.lexmark.com), then the only thing I would suggest is to enable the Administrator account on your Vista computer and then you will be able to install the driver/software for the printer from your original install.
Activating the “Administrator” account and using that account only will make your Vista machine faster, safer, and you will no longer have those extremely annoying “UAC (User Account Control)” windows that freeze your computer and ask you to allow or not allow a program to run. This is just another alternative to getting rid of Vista. Here is the best link I could find on how to activate the true “Administrator” account in Vista home: http://www.howtogeek.com/howto/windows-vista/enable-the-hidden-administrator-account-on-windows-vista/
Glad to help.
Feel free to email me if you have any more problems
sewellp@yahoo.com
Patrick Sewell, February 2008