Airport not working with PC

Hi guys! I have a very stange problem here. We have an Airport Express, 2 Macbooks, 2 iPhones and an Acer Aspire One netbook with XP. The thing is every Apple device connects to the Airport with no trouble at all, but the Acer machine drops connection after 5 minutes of activity online. The strange thing is, its still connected to the Airport, but can't browse the net anymore. I have tried everything on earth, but no luck. Just for the record, the Acer worked everywhere else. Sometimes we connect to next door's unsecured networks and no trouble for hours. So it seems like there is something with the Airport. Any ideas?