Here is a solution (credit given to an Ubuntu forum entry) that I just tried and it works for me on Mint 7:
You can make nm-applet not use keyrings to connect to certain wireless hotspots - therefore you don't need a password to unlock the keyring thing as it isn't needed.
Right click on nm-applet -> "Edit connection"
Go to the "Wireless" tab
Click on the wireless hotspot you want to automatically connect to
Click the "Edit" button
At the bottom of the window, you should see a tick box which says "Available to all users".
Tick it and click Apply!
You can now auto-login without having to enter the keyring password every time without any workarounds whatsoever.
"The Second Amendment isn't about protecting ourselves against criminals. It's about all of us protecting ourselves from all of you." ---Dr. Suzanne Gratia Hupp to Congressman Charles Schumer (D-NY)