seems you just need the non-free firmware. See for example https://wiki.debian.org/iwlwifi
However if you don't have some other means (eg wired connection) to get online you might not actually be able to follow those instructions. In that case, download the .deb file using some machine that does have an internet connection and then transfer it your Debian machine using, for example a usb stick. Then install the .deb file. You can find a link to the .deb file at:
(I'm assuming you are using Debian wheezy).
Post back if you get stuck and tell us what the problem is.