Security

your computer if Wireless is disabled...even if it is enabled then how?

So far I believe you should not have windows selected to connect to wireless networks automatically. Keep it disabled all the time.

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There is no proven way to prevent anyone from accessing a computer through any working WiFi Adapter.

You can however make it more difficult for people who want to do this by employing WEP, WEP2 and various other Security that is supported by the WiFi Access Point or Router.

Col

Use infrastructure mode (instead of ad-hoc).
Use the strongest encryption supported by your wireless network (likely WPA2)
Don't connect to unfamiliar/open wireless networks.
Use a personal firewall.
Disable any network services you don't need

My farthest user connects well with 2% signal strength so my thinking is that there isn't any need to have a signal farther beyond them.<br>
Depending upon how many users need to access shared folders you could password protect the folders too. If there are more than a handful of users it'd be cumbersome.