hi all .. many people were wory about that ubuntu don't support their internet wireless card they .. i had had the same problem .. but no it's no more ...!
well in 8.04
i did the following :
1-in terminal :
that to list ur USB devices
and here u will have a list of ur usb devices..
sudo modeprobe usbserial vendor=xxxx product=xxxx
the xxxx should be filled from the list that u got from the first step..
3- then use Kppp or gppp to add ur configurations ..
note that may not work from the fist time and u may need to restart ur system...

and for 8.1
u don't have to do none of the above .. just in the network settings add ur username and the password to the ppp connection and that is all!

and good luck!