To configure SourceSafe to use DiffMerge open the Tools | Options dialog and go to the Custom | Editors page.
First ADD an entry for Operation File Difference.
Use file extension .* and set the
command line to:
C:\Program Files\SourceGear\Common\DiffMerge\sgdm.exe
/t1="original version" /t2="modified version" %1 %2
Next ADD an entry for Operation File Merge with the command line:
C:\Program Files\SourceGear\Common\DiffMerge\sgdm.exe
/t1="source branch" /t2="base version" /t3="destination branch"
/result=%4 %1 %3 %2
