I have a P5Q with Vista 64 and have a problem losing network connection as well. This started happening a day after assembly. Sometimes it is there at start up and other times not.
Driver updates haven't solved it, however, I found that I can get connection when it fails by starting the Atheros Utility. And I don't seem to lose it again unless it fails to start at reboot.
I've seen several posts on this type a problem with this MB, but no solutions yet.