just go into device manager (right click my computer, manage) and uninstall the network driver. FIRST though make sure you have downloaded the new driver from at least 2 sources because one of them is bound not to work and if you dont have a network driver you cant download another one

unless of course you have another computer at which you could try a few. drivergenius and everest are programs that can determine your hardware and give you links to where you can download drivers from. gateway will likely have your driver on their site so look their first after putting in your computer model.
edit:
http://support.gateway.com/support/drivers/dlcenter.asp enter your serial number and go to drivers and downloads. then network drivers. download and run. gateway drivers have been tricky for me in the past, so read the README file that comes with the driver. that ought to do it for you.