Would you run the lspci command from a terminal and post the output of it here? That should report the wireless chipset.
Please surround the output of the lspci command in code tags, which are available when you click the "Go Advanced" button at the bottom of the reply window.
This post from Dell
would seem to indicate it's a Broadcom chipset. If
that's the case, the required drivers are available in the Ubuntu repos. You would need to open the Synaptic package manager, go to Settings-->Repositories-->Ubuntu and enable the Proprietary Drivers for Devices (I think that's the wording) repo. Search for Broadcom. The drivers should be there.
Edit: *.inf files have no meaning in Linux world unless you are using ndiswrapper