I'll explain. Vista uses the User Account Control. This forces you to do certain things as an Administrator. For the programs and games that really don't need to run as Admin, Vista creates a VirtualStore. This is a location you, the user, can read and write files to. This is what happened with Gothic 3 in Vista.
For get around the problem of not having access to the console, Press the Windows Key on your keyboard. Hold that and press R. This will bring up the RUN box. COPY and PASTE the following INCLUDING THE QUOTES into the RUN box. Press enter.
"C:\Users\%username%\AppData\Local\VirtualStore\Program Files\Aspyr\Gothic III\Ini"
Edit the ge3.ini in there.
You MAY want to copy the ge3.ini from the game directory to copy over the changes the Community patches made and then edit it from there.
Let me know if you still have problems...
I did a search and did find in c\program files\aspyr\gothic III\ I did find several .ini files, but none of them had test mode listed in them.
I just reinstalled windows Vista and installed the game in a separate directory c:\Games\Gothic 3\ and Vista does not force the game to create the VirtualStore directory.
One thing I noticed is you typed Test Mode. It's TestMode - No space.