In the Wi-Fi utility for the Netgear adapter, you'd typically have an option similar to wireless survey which eill allow you to monitor the signal strenth and quality of the connection.
Can you monitor the above-mentioned parameters and revert with the observations?
Also, is the problem occuring on a particular O/S or is common?
One more thing, If your machines have a built-in wifi adapter, have you tried connecting the same over 802.11N?
Warm regards,
Sarang