Can't connect WAG160N to the internet

Hi everybody,

Friends of mine have just bought a LinkSys WAG160N to replace their
current DSL modem and wirelessrouter, which they asked me to install. For
what it's worth: they have a Belgacom ADSL internet connection.

I disconnected the incoming cable from the DSL modem, plugged it into the
WAG160N, and hooked up the four ethernet cables from the router to the
WAG160N as well. After turning on the power, the power led started
flashing, and the WAG160N indicated that one computer was connected (the
others being switched off at the moment) and that wireless was available.
No internet connection, though.

After checking the single computer that was turned on, I could see that
it had received an IP from the DHCP, and that I could see the router
perfectly well. Still no connection to the internet though.

There was an install CD within the box, which I've tried. It failed,
stating some obscure message about the windows installer service. After
several attempts, it still refused to install, and I started to try the
LinkSys assistant (sorry, forgot the real name) to connect to the
internet. By following all the steps (powercycling the router etc...), I
still was not able to connect to the internet.

At the moment, I'm at a loss as to what I should do next. My own
connection at home is a cable modem - sometimes it helps to wait an hour
or so after switching devices, so I gave them the advice to let it all
rest for a few hours and try again. Besides that, I have no idea as to
what I should try next.

Is there something I missed, or is there a problem with this particular
router? How can I get this router up and running?

Thanks in advance!

Ikke