Diff
Program: C:\Program Files\Beyond Compare 3\BComp.exe
Args: %1 %2 /title1=%1 /title2=%2
Merge (for doing three way merges)
Program: C:\Program Files\Beyond Compare 3\BComp.exe
Args: %1 %3 %2 %4 /title1=%1 /title2=%3 /title3=%2 /title4=%4
I know the args list looks a little wrong but this version will prioritise your local copy of the file over the head of the branch (cause you don't really want to loose your changes)
Hope this helps...