Im assuming that you have a WindowsXP pc connected to this router when I say the following

if you go to 'run' and type 'cmd' the command prompt windows (black box) should then show.
in this window type 'ipconfig' this should then list your network configuration... the ip address for your default gateway should be displayed.

This is your router ip address, type this into your browser ( ie http://192.168.0.1 ) you should then be prompted for the password, the default user is usually 'admin' or 'user' and the password 'password'

you should then be able to see your router configuration