Is it a built in network card? If it is you can get the driver from dell.
If you have access to a computer with internet, you could download the drivers on to a usb stick from the Official Dell Site
. Then install the drivers onto the laptop from the usb. BTW the link is for the UK site, you will need to change the location at the topof the page if you are somewhere else.
Here's some instructions to do this if you need them:
Click on "I'm looking for drivers and downloads" then identify your laptop using one of the three methods dell gives you (first or second are probably the easiest).
Then when you've identified your laptop select your operating system and what driver you need from the dropdown lists (network). A network driver should appear below. There will probably more than one.
Select the one for your ethernet adapter on your laptop. Make sure it says "Dell-Driver" in the title (not update or something).
Click download and then 'download through your internet browser'. It should end up in the downloads folder (if using vista or 7) or you will get asked where do you want to put it (if you're on an xp machine). Make a note of the file name anyway so you can look for it.
Then drag and drop the driver file onto the usb stick. Then simply put the usb stick into your laptop and double click the driver file and follow the prompts to install it.
Hope that is helpful.