I downloaded the tkdiff kit for Windows from the Georgia site. It gives me a zip file, which I open. Inside are 3 files: Changelog, COPYING and tkdiff. These files have no extensions and when extracted have no associations and don't do anything. I first did this a year ago with 4.0.2 and today with 4.1.3 and am not able to get anything functional. How do I extract the kit and get it working?
I might have put a suffix of .tcl on the tkdiff, or it might have unpacked that way. I probably put a suffix on it in my efforts to get it working. Either way, find your wish80.exe and make sure it is in your $PATH, then try the command I gave you before, ie. execute wish80.exe and give it a argument #1 of the tkdiff file that you have, then the two files to compare.
wish80 \full\path\tkdiff file1 file2