This is probably not a Mint issue, but maybe someone found an answer since the last time connection issues with the LiveBox modem came up ...
I'm pretty sure that I could connect to our LiveBox 2 (Sagem brand) wifi router last year, from Windows as well as from Mint. Since, I haven't worked under Linux, and now I can no longer connect to the router when not booted into Win7. Key and ESSID haven't changed nor has my MAC address, but the modem's firmware has. This problem exists with several other Linux distributions (but not that other Unix desktop OS, Mac OS X). I can however connect to my Apple TimeCapsule router, connected to the LiveBox via ethernet and just acting as a proxy so it's still the LiveBox that hands out IP addresses.
The computer is an Acer Aspire One A722 with a Broadcom Corporation BCM4313 802.11b/g/n Wireless LAN Controller (rev 01). The kernel is one I build myself (3.2.21 with xenomai extensions and the brcmsmac Broadcom driver).
But as said, I've recently toyed with the latest PearOS as well as the BackTrack hackers distribution, and both were unable to connect.