i make my livecd using a live-helper tool.and install it on a virtualbox.now problem is that mylive cd(without graphics) is not dectat the internet ? anyone can give me suggestions plz?

DId you enable contrib and non-free in the repository? Have you installed the correct drivers?

First is first... Can you ping any site? Do you get "unknown host" error when pinging? If yes, then you need to change in Network settings of the virtual box "Attached to Bridged adapter". If you don't get the unknown host problem meaning that you can ping sites than you need to do what k3lt01 said: Go here, choose your country, release etc... Click generate list and copy everything to sources list...
Or you could just do this (as a root):
And comment out the line with the cd-rom by adding # in front of that line. Then at the end of other lines starting with deb and deb-src add contrib and non-free. Save the file, run apt-get update and you should be god to go...

Good luck!

zk04 yes i dont ping any site,even google and recive the error as a unknown host.and i use a mobilebroabband connection for a internet. now what can i do ?

When in Virtual box click on settings, now go to Network settings and change the Attached to Bridged adapter... restart virtual machine and try pinging Google again. If that doesn't work, change it back to NAT and restart virtual machine. Let us the result. Do you get errors again?