I have recently installed an opensuse 11 system on my friend’s computer with a live CD (he doesn’t has a DVD), but the problem is that he has a router, and I couldn’t connect to the internet because I don’t know how to install a router in a linux system…
The router is connected tough a network.

Can someone help me?

Connect the ethernet cable between router and wired ethernet card on the computer. Setup card in Yast for DHCP and there it is.

More details here:
HowTo Configure a network card in Suse/openSUSE 10.x for LAN and Internet Access.