Hi,
There are a number of things that can cause a drop in strength
including the weather. It is very important to ensure that access point
is in a central location. Do you have any electrical devices that could
be causing interference. Is there anyone else locally with a wireless
network.

The ADSL is totally seperate to the wlan.

I have worked with a number of wireless kits and I now only use D-Link
as I have found them to be the most reliable. Check that you have the
latest firmware and that the card is compatible.

Are you using XP with sp2 as it causes a lot of problems with WLANs if
they are configured manually (Properly)

Try resetting your access point.

(Just a bit of a dumb question, but you have switched off your old
router)

Heres a bit of a hack. Use your old router and connect your adsl router
into it. Switch of the access point.

HTH
Alex