CsDiff is used as an external program to display the difference between different versions of a file. You can use it to find the changes that were made. There are a couple of (free) programs you can use, I used CsDiff version 2.5. It is a free tool and it worked for me. You can download it from the ComponentSoftware website.
Download CsDiff from the ComponentSoftware website
No real setup needed, just unzip the files to a directory.
You need to tell WinCVS were it can find CsDiff.
Start WinCVS
Select Admin > Preferences
Select tab WinCvs
Check the box in front of "external diff program"
Click on the browse button and select the CsDiff program
Click on the OK button to apply the setting
You've now configured CsDiff