Set your home environment. You can do it at the commandline:
set HOME = c:\
That only works as long as that console window is open.
For a more permanent solution, you can do it via the environment settings (right click My Computer, choose Properties, choose “advanced” tab, select “Environment Variables” and create a new UJser variable. Make the name HOME and the value c:\
You will not need to restart your computer but you will need to close any open console windows for those changes to take effect
That should help. (Not tested, but I know for a fact that the ZenTest gem makes you do the same thing on Windows.)