Updating drivers usually doesn't affect the hardware itself. Its strange that it simply stopped working because you installed vista drivers on another computer. My Pixma was simply a plug-and-play from my vista desktop to my XP laptop.
Can you provide more detail? Does the computer detect the printer but it simply doesn't print? Or is the printer undetected completely? Maybe you could try uninstalling then installing new drivers for it.
I did as you advised, and uninstalled and reinstalled the software for the Canon Pixma mp780. The laptop with XP recognizes and finds the printer, but when I ask it to print, it makes the attempt and comes back with the message "failed to print".
I have used this printer on the laptop for a couple years now, and it just pulled this stunt after I purchased a new desktop with VISTA and had to find a new driver for it.
I am going to assume this printer hooks up to the laptop via USB cable. What happens if you plug the printer into a different USB port? I would assume Windows XP would see it then reinstall the printer for you use.