I also agree with Archeon. Especially if your wireless devices are different brands. I had what sounds to be the exact same problem using an Orinoco silver PCMCIA card with a Linksys WAP11. With WEP enabled the the Orinoco card would spontaniously be unable to connect to anything, connections would just timeout. It was still connected to the WAP with excellent signal strength, but the WAP wasn't forwarding the cards transmissions. I spent quite a while dubbing around with settings and installing the latest drivers. Disabling WEP was the only way I could get it to work. I have since sold the WAP11 and bought an Orinoco WAP and now the system works flawlessly.

Interoperability sucks. (in my opinion)

-Jeff