If you haven't already tried this maybe it will work for you.
- Put the tablet into APX mode, then plug in the USB. Windows7 will drag on then fail installing the drivers, as usual.
- Go to Control Panel->Hardware and Sound->Device Manager and find the '!' (unknown device)
- Right click and choose Properties, then Uninstall Driver (if it is an option)
- Next, click on Update Driver, then choose Browse My Computer ...
- Navigate to the NVFlash folder (the one you extracted from the nvflash .zip you downloaded)
- Open the folder inside called 'usbpcdriver' or similar, and select the .inf file (NvidiaUsb.inf) and choose to install it. Once it installs, it should recognize the tablet as a MTP device. If not turn off the tablet, unplug the USB, restart Windows and plug it back in when it is finished rebooting and start the tablet in APX mode again. If it still doesn't recognize it try the whole process over agian.
I can understand being hesitant toward running Linux but running from a flash drive or in a VM is pretty safe, as in if you mess up the OS you can always start over without damaging Windows. Done it many times! Try running Ubuntu in a virtual machine such as Virtual Box, it is almost as user friendly as windows and you can have the VM capture USB devices such as the Gtablet which Ubuntu should recognize. Probably won't run very fast on a laptop but if you have at least a dual core with 2 GB of ram it should be pretty smooth.
Not trying to push Linux on you or anything, just some suggestions. From what I hear most of the Gtab devs use Windows7 and it seems to work great for them!