Hey all, I've spent DAYS banging my head on a desk trying to get my new install of Squeeze working on my T520. Two major issues: the wireless card was not recognized, and the screen resolution could not be changed (among other things, like not being able to change brightness, being unable to wake up from sleep, etc. etc. etc. If you're here you probably have some idea of what I'm talking about).
My first line of attack was installing the correct drivers. lspci -nn showed me that my network card was something along the lines of Intel Wireless 6000 Gen2. Installing the right drivers didn't help. Installing from backports didn't help. The network was always listed as unclaimed. Wlan0 was no where to be found.
The solution that finally worked for me: upgrading the kernel from 2.6.x to 3.2.0-0.bpo.4-amd64. The guide I used for this is here: http://www.cyberciti.biz/faq/debian-...ux-kernel-3-2/
This fixed everything: wireless issues, Xorg issues, all of it. So if you're in the position I was in, maybe try this as a first line of attack before tearing your hair out over config files and drivers. One other bit of weirdness, my network card is now recognized as Intel Centrino Advanced-N 6205. Don't know why that is.
I hope this helps someone out there!