Windows 7 Windows 7 and WDS weirdness

Having a very strange issue with Windows Seven machines and connecting to a wireless network with range extended via WDS.

The scenario - shared accommodation with internet access provided via wireless. Base station is an Airport Extreme, with Airport Expresses used to expand net coverage throughout the building via WDS. I don't own or control any of this hardware, and access to it is limited - that said if I need to find something out I'm sure I can ask nicely. Machines running Windows XP, OSX or *nix (Debian and Ubuntu) can see and connect to network anywhere just fine, have average signal strength of 70-80% throughout. The two Windows Seven machines, however, seem to completely ignore the WDS'd network, and can only pick up on the presence of the network when in close proximity to the Airport Extreme base station. It's as if the Airport Express repeaters simply didn't exist.

I can't find any common factor here other than Win 7 - one machine (desktop) was running Win7 Pro x64 with a Linksys USB dongle, the other is my newly-bought netbook running Win7 Starter x86 using (I believe) an AzureWave half-mini adapter. I've borrowed another Belkin dongle to try in desktop and lappie, with the same results - the repeaters may as well not exist. I'd initially put it down to strange behaviour on the part of my desktop rig, and worked around the problem by running a long length of CAT-5e from my desktop to the ethernet port on the closest Airport Express (which worked fine, although slowly), but now I've two machines having the same problems this really isn't an option any more.

Anyone have any ideas? Google-fu is failing me on this one, and it's really quite frustrating.