Can I use my Android device as Wi-Fi Adapter for my PC (i.e. Tethering to PC through USB, but using Wi-Fi not Phone Network)? I want to use my Android phone to connect a desktop (windows 7) PC to the internet via Wi-Fi (ie, not muching though my Data plan). Is this possible with the various tethering options out there?

The reason I ask is, most suppot wi-fi the other way around, ie, the phone is the wi-fi hotspot, and the internet connection comes over the phone network. I want to connect to an existing wi-fi network, and share that with the PC.

Background - for various reasons our office LAN network is b0rked and very slow. The office WiFi network on the other hand is happy and fast. But my desktop PC is wired only. If I can use my phone as a wifi dongle/modem/adaptor, and connect to the office wifi, then I'll get a much faster connection.

Edit: I've got an HTC Desire HD, I haven't rooted it so far.
You can achieve this natively on some versions of Android (for me it works on KitKat 4.4.4). All you have to do is connect the phone to wi-fi as usual and then connect the USB cable and do a USB tether. Some devices may require you to enable WiFi sharing in the mobile hotspot settings. Your computer should detect a new hardware - a &quot;USB ethernet&quot; or similar, you may need to install drivers for that, ymmv. Then it behaves just like any other network card. This works for all common operating system, including Windows (where the drivers part may apply).
Just to be sure, you can disable mobile data on the phone for the time being but the phone should be smart enough to route traffic via wifi automatically when it is available.
No root needed.