Hi,
I have two machines both running Ubuntu 9.04. I have a Mobile broadband connection and a wired LAN between the two machines.

However when I connect the LAN, I am unable to use Mobile broadband. When LAN is on I am able to connect to the Broadband and get the IP address, but when I try to ping any site it does not respond.

I tried by connecting both the connections using NetworkManager and also by connecting Broadband by wvdial and LAN by NetworkManager but same results...

Where am I going wrong ?

I am a complete newbie to Networking stuff.

Thanks & Regards,
Vineet

Why would you want to run two network connections at the same time? the tcp/ip stack will take the default one, in your case most likely the LAN connection.