The Dell Lattitude series of laptops (D630, D830, others) use the Broadcom 43xx series WiFi cards. These have firmware that is proprietary and needs special voodoo to make work.
The answer is scattered around the interwebs and I can never find it on the first go, so here is what works for me.
First off, if you are using Linux Mint in the control center there is a Driver Manager. Do not use this to enable the Broadcom card, it does not work. (The Nivida driver does work however.)
What you need to do is as follows:
apt-get install b43-fwcutter firmware-b43-installer
Then edit /etc/modprobe.d/blacklist.conf and comment out the bcm43xx line
You should be able to unload and reload the modules with:
modprobe -r ssb_hcd modprobe -r b43 ssb modprobe b43
The wireless should just start working and network manager should start showing wireless networks!