You would most likely have to find the gateway of your PC and then put that in a browser. Once you're "in" your modem, their should be a menu in there that'll let you configure settings like Static IP's and the sort...

How to find Gateway...

START, RUN, type " cmd "

Then type " ipconfig " in the box that pops up.....should show you your IP address, Default Gateway, and subnet mask....

The Factory Default Username is :

Administrator

and the password is left blank