So this has been REALLY frustrating me. Any time my machine sleeps the Wifi doesn’t work on resume and I have to reboot.

Given the propensity of Windows 7 to sleep given any chance whatsoever (power saving madness!) this became quite infuriating. It' seemed to happen on both my machine, an HP and a Lenovo- with different drivers on each.

In the end I’ve traced it to the Virtual Machine Network Services feature on the WiFi adapter:

Disable this and everything works really well again. These get installed with Virtual PC 2007

Hopefully this helps and has sufficiently GoogleJuicy keywords in the title!