you should use http://192.168.0.1/
if you are using windows
Go to start menu/execute and type "cmd" a new black window will appear type "ipconfig"
you should see information about your connection beside default gateway if you see 192.168.0.1 the url stated above should work. If you don't see that you are NOT connected to your router...
-- You obviously connected to the internet.. try unplug the modem from your computer and plug the modem to the router... If you have some more wire plug your router to your computer and retry ipconfig... you should be OK then...
If this does not `t help.. try to put more information in your post..
-- OS version ( mac, XP, VISTA ... )
-- what did you try ?
-- Is your computer configured to use a static IP or DHCP
-- the printout of ipconfig
Hope this is enough