Define new external tools in eclipse
1. Select Run -> External Tools -> External Tools Configurations ...
2. Click Program in opened dialog
3. Type "C:/Program Files/cvsnt/cvs.exe" in Main -> Location
4. Type "${selected_resource_loc}/.." in Main -> Working Directory
5. Type "diff -u4 ${resource_name}" in Main -> Arguments
6. Apply the change and close the opened dialog.