i have exactly the same issue with windows 7. updated all driver but the zotac wireless adapter is flakey and when it does connect it is very very slow. Cant figure it out. Ive dealt with these many of times and i cannot see anything other than the adapator or some strange windows 7 compatablilty issue. Have 3 other wireless devices that are perfect.
Never got it to work properly, even with a new Win7 7600 install. Instead bridged my o2 wireless box, hooked it up to a DIR-655, and bought a wireless n adaptor for the Zotac. Got reliable GigE and wireless n now, miles better. That via wifi card really is a PoS.