Look in the control center for something called "Additional Hardware" or some such name. Click on it; if you need a proprietary driver, it could well install it for you (this worked on my Dells with Ubuntu).
Since it's a Dell, there's a good chance you have a Broadcom chip; Dell likes Broadcom. This post will give you the tools for checking that out and some tips for getting Broadcom to work:
It will also tell you how to determine what wireless chipset you have, which is essential information for further troubleshooting of this issue.