You need to hit www.dell.com and use the Support link. Your Dell has a service tag # on a sticker, probably on the bottom of the unit. Enter the Tag # and you are given a page with links to all drivers for the OSes that unit supports.
Or, call dell tech support at 1866-516-3115 and have the tech help you out. Just give them that #. They will help you find a driver even if it is out of warranty.