Is it a laptop?
It's probably got the 1100 series card in it. If it came right from the factory, you won't have to install any drivers - otherwise, go to http://support.dell.com and grab 'em.
Once you've got that, go into the Router's setup screen. You want to find the wireless settings. Make sure you're not broadcasting your SSID and change it to something unique (if you haven't already)
From there, you want to set up WEP. Depending on the router, you'll have a choice of either 64 or 128 bit OR both. Take the highest available. You'll be asked to create a key - think of it as a password and make it good.
Once you've got all that setup and saved, reboot the router. Take the SSID and key to your laptop and open the wireless card properties. Click ADD, put in the SSID and key when prompted.
With any luck, you'll be online at this point.
Let me know if you require further assistance!