Just a quick update after all my laptop wifi woes:
I sent the laptop to the client with the 3COM card, which here in the office had been taking ages to connect requiring re-entering WEP key details, despite them having been stored in KWallet.
Well it turns out that when he got it home it connected straight to his AP without problems, so whatever was wrong was either my office or my AP.
Thanks for the network manager suggestion - that made the process cleaner. I'm now trying to find a USB wireless dongle I can rely on in Linux for future.