Tarbat,
From what I understand, for security reasons from Vista onwards, Microsoft limited the number of wireless connections, (through the tcpip.sys). There are a couple of tcpip.sys patches on the internet but none of them worked for me. In fact, they totally messed up (putting it politely) two PC's (Vista and Windows 7), to the point where you couldn't even reboot. To change the tcpip.sys file I ended up having to take the HDD out, and then connected it on to another PC to gain access to the file.
If you Google tcpip.sys there's a lot of info on the issue.
I think I also had some trouble with it when plugged in to the USB port as well.
Andrew