I've Xubuntu 12.04 installed on my HP DV-4 laptop, and it was working fine with my previous wifi router - a Buffalo Air Station WHR-HP-G54.
I recently replaced the Air Station with a new Netgear WNDR-3800... basically gigabit ethernet ports, added multi-band 802.11n, etc.
Everything in the house has been reconnected to the new network - iPods, iPhone, Kindle Fire, Macbooks, even this HP DV-4 laptop - when it boots in Windows Vista 64.
When in Xubuntu 12.04, Network manager 'sees' the network(s), just as before... but cannot connect to them. It just sits there with the icon 'spinning' until it times out.
Regular 'wired' connection works fine... just can't seem to connect to the wifi network(s) - any of them.
Shouldn't be anything 'special' required; none of the other devices needed anything other than the new password to connect.