Bit drastic to want to disable the USB ports isn't it? Whilst it is entirely possible that a virus could be transferred by USB it is a bit unlikely.
There isnt a foolproof way to have your cake and eat it, seeing as most viruses transfer via the internet and as you have suggested the anti-virus doesn't have an internet connection to update then it is highly unlikely that a virus will be transmitted to the laptops whilst they are off the web.
Urban Kaos
November 2007