skin.....it's not that :PPP

is this only on the ubuntu install? or is it also on the mac install?
linux doesn't handle certain wireless cards that well.
make sure you have wireless-tools installed

sudo aptitude install wireless-tools

(on another note, use aptitude instead of apt-get, most will tell you to use apt-get
but it doesn't remove dependencies, so if you along time with one install, you could
end up with a shitload of dependencies you don't need)

other than that...i dunno, try using ndiswrapper, if there's windows drivers available
for your card

install ndiswrapper (sudo aptitude install ndiswrapper(not the name but i forgot what it
was in the repo)

then extract the drivers, cd over to the dir

sudo ndiswrapper -i THEDRIVER.ini
sudo depmod -a
sudo modprobe ndiswrapper
iwconfig (check to see if it's connected)
sudo ndiswrapper -m
cat /etc/modprobe.d/ndiswrapper

you could try these 2 first, it restarts the wifi card.
sudo ifdown wlan0
sudo ifup wlan0

sudo iwlist scanning
sudo dhclient wlan0