I've been running Vista on a Toshiba M5 for quite some time. Since the RTM, the drivers for the 3945ABG driver from Intel have been garbage. Tried each one as they came out from Intel's site here:
http://downloadcenter.intel.com/Filter_Results.aspx?strOSs=All&strTypes=All&ProductID=2259&OSFullName=All%20Operating%20Systems&lang=eng
So, back in late August, I was checking Dell's support site on a different machine and noticed that the drivers that Dell was publishing for the Intel 3945ABG were a later version. Intel's site didn't have them - nor does Toshiba.
So, since then, I've been running with the drivers (which are built by Intel) from the Dell site for the 3945ABG from this link:
Installer package for driver version 11.1.1.22
Haven't had a problem since. There used to be issues that would intermittently drop the connection forcing a manual reset with the HW switch on the outside of the M5. Even one error which showed up in the event log that was only addressed by a reboot. It was so bad I pulled out an older PC Card WIFI adapter to use until I was able to reboot.
I don't get Toshiba or Intel - I've found this error posted across many forums, Technet. Microsoft, Ars Technical, Vista Forums. This is the state of affairs when it comes to quality and support and why these guys are failing.