If you have a Cisco IOS style router then this will help you get the basic configuration configured to get online.
You should change the following items in the configuration listed below, if you copy and paste this configuration it will set the router to be on 192.168.0.1, once connected to the internet you should conduct a security scan to make sure your router is not open to the world:
ISP_USERNAME – The username as supplied by your ISP
ISP_PASSWORD – The password supplied by your ISP
MY_ADMIN_PASSWORD – The administration password you would like on your router
line vty 0 4 password 0 MY_ADMIN_PASSWORD login interface ATM0 no ip address no atm ilmi-keepalive pvc 8/35 encapsulation aal5snap protocol ppp dialer dialer pool-member 1 ! dsl noise-margin 3 dsl bitswap both interface Vlan1 ip address 192.168.0.1 255.255.255.0 ip nat inside ip virtual-reassembly interface Dialer1 ip address negotiated ip access-group FW in ip nat outside ip virtual-reassembly encapsulation ppp dialer pool 1 dialer idle-timeout 0 dialer-group 1 no cdp enable ppp chap hostname ISP_USERNAME ppp chap password 0 ISP_PASSWORD ppp ipcp route default no ip http server no ip http secure-server ip dns server no ip nat service sip tcp port 5060 no ip nat service sip udp port 5060 ip access-list extended FW deny ip any any ip nat inside source list 1 interface Dialer1 overload access-list 1 permit 192.168.0.0 0.0.255.255