If you're connected to a router trough the usual ethernet cabling (RJ-45...), then it shouldn't be a problem. Do you know the device it uses to connect? It's probably eth0 (especially if you only have one ethernet card), but make sure. After you know that, simply issuing (as root)
or if you have dhcpcd instead of dhclient as your DHCP client,
and a short moment's wait should send DHCP requests and get the answers (provided that there is a DHCP server at the other end of the cable, which there is if your other operating systems work via dhcp). Try both dhcpcd and dhclient if you have them, or then the one you have.
It really is that simple - provided that the device works. If dhcp doesn't work, and neither does static address configuration, probably there's something wrong with the device (i.e. between the device and your operating system).
ifconfigh eth0 down #brings interface down
ifconfig eth0 up #brings interface up
dhcpcd #(or dhclient) configure the device via DHCP