Hi djmykey,
Which model is your modem/router?
If the manual says you must enter the IP address 192.168.1.1 in your browser you should be able to access it.
First make sure your computer is set to the same IP range as the modem/router (for example if the router has the address 192.168.1.1 then your computer should be in the same range). Are you using Windows XP?
Go to My network places>Local Area connection>under general go to the TCP/IP protocol>Properties> Set the IP as say 192.168.1.2 subset mask 255.255.255.0 and then under DNS settings, enter the IP (192.168.1.1) of the router as the preferred primary DNS.
Disable any proxy setting you might have entered in your browser (IE, Mozilla etc). Select it to detect connection automatically or specify it ...direct connection to the Internet.
Now when you open your broswer and enter the modem's/router's IP, you should be able to access the router's administration screen. Enter the default user name and password here (refer to the manual). You should now be able to see the router settings. You may want to enable DHCP if you like (so that the IPs will be alloted automatically to all PCs on your network). If you enable DHCP, once you exit your router settings, do make sure to come back to your network settings on your computer (the computer you used to access the router settings) and change the manually-set IP that you did previously to access the router --- to obtain an IP automatically, i.e., revert back from 192.168.1.2 to Obtain an IP automatically.
Make sure to change the administration password for the router before you connect the modem to the Internet.
Read and re-read that manual. It should be all there.
DH