trying to install windows 7 pro on my IMAC using bootcamp assistant.

When I get to the point of installing windows and loading drivers from the data downloaded for windows support from Bootcamp, I get an error message that the 4 USB Universal Host Controller drivers for the Intel 5 Series/3400 Series Chipset family cannot be installed. It is telling me to contact my vendor for an updated driver. I have looked everywhere and can't find such updated drivers. Can anyone help?