Problems with setting up a home network.

I am trying to set up a network between a Vista desktop and an XP laptop.
The network contains a D-Link router, which has both ethernet and wireless
connections. I have the desktop connected to the router through an ethernet
cable and the laptop has a built-in wi-fi capability. I have been using the
router and the laptop together for months to connect to the internet with no
problems.

When I first tried to set this up, the network and sharing window showed all
the components, i.e., the PC, the router and the laptop. When going through
the set up a connection point wizard I got the message that the network had
been detected but would have to be set up manually. Proceeding I got a
window which asked for a user name and password for the router. I've never
set up either on it. I can't get past this point.

Secondly, when trying to troubleshoot the problem the documentation says
that all the computers needed to be on the same workgroup. The laptop was
using the default XO workgroup name, so I changed it to the same name as the
PC. Now the sharing view only shows the router; the PC and laptop have
disappeared!

Can anyone help me?

Thanks in advance for any help you can give me.