In such a case there are no vista drivers avaible as well. That is the whole idea why the vista and xp support was removed from 10.8
Newer hardware does not have any driver support anymore for those older windows systems, thought I complettely agree that it is super annoying for such cases when you actually have to right drivers for your hardware, but are unable to simply start the installation because you updated your OS.
By the way, you can initiate a windows 7 install in mountain lion and than simply switch the windows dvd out for the XP or vista one when your system reboots. Bootcamp drivers can be installed from an old osx dvd or a old bootcamp download. This again requiers that your hardware actually is supported by older bootcamp versions and that you have access to a win7 install medium.