[Hampshire] WiFi problems

Help! I'm struggling with a Wifi connection at the Guest House I'm staying
in, and I, the landlord and another guest have been trying since the New
Year to re-establish my connection, with little success.

In 2007. Using my own dual-boot WinXP and Ubuntu laptop, and also the
company's WinXP laptop, I was able to connect to the WiFi with no problems
at all.
Over 2007 Xmas/New Year break - a full-time guest installed an extender so
he could get access to the WiFi at his accommodation in an adjoining
building.
Jan 2008, I return in the New Year with just the company laptop and it can't
connect. I return the next week with both laptops, and again I can't
connect. I examine all settings on the lappies for the wireless receiver and
the wifi network, but all is okay. I consult the permie guest who denies
changing anything except the channel. I try connecting from his digs with
success, but on return to the room, nothing! I tried at a later date from
his room but I have been unable to attain the connection again.
At first Linux would not connect, but now it does. So hoorah for Linux and
one in the eye for Windo$e.

So to summarise, I can't connect using Win XP from either laptop. They can
see the network, so they don't have faulty wifi equipment.
My own laptop will jump straight onto the network when running with Ubuntu.
Both laptops connect to my home WiFi, and the company one connects to the
company WiFi.
No-one else in the Guest House is experiencing the same problems.
I have checked the router and all settings look okay. It does not restrict
specific mac addresses only to connect (if it did, Ubuntu would not
connect).
The signal is medium to strong!

I have tried everything I can think of, including deleting the network from
my preferred list and allowing it to be re-detected. Does anyone have any
ideas what else I could try?

Thanks, Kelvin

Broadband provider is BT.
Equipment: Router is a BT Home hub (Speedtouch)
As of 2008, a booster (don't know the make or model), was added by another
guest. It connects to the Speedtouch using wireless.
Security : wep (and I have the correct key)