I recently installed Ubuntu Hardy Heron on my PC and loved the performance even after it was installed using Wubi as an application within Windows. I then wanted to use the internet on Ubuntu. I have a Reliance Wimax connection (I have since moved to Airtel due to the lousy service Reliance gave me). When I checked the network configuration on Ubuntu, I saw that there was no network connection. Logged back into Windows and Googled for some information. Came across this information given by pk_rulz on the Ubuntu Forums. He advises that the problem was due to the avahi daemon assigning an IPv6 address to the eth0. He advises:
Bring down avahi daemon using
sudo /etc/init.d/avahi-daemon stop
sudo ifconfig eth0 down
sudo ifconfig eth0 up - this is basically to restart ur eth0
I did the same and I am now able to use Reliance Wimax on Ubuntu. (Not anymore. Reliance Customer No Care has since made me so frustrated with their service that I have moved to another provider).