Musing's from teh M^onk^K . : . who knows what a programmer thinks? . : .

Since I always forget the settings, here they are :-)

From: http://www.scootersoftware.com/download.php?c=kb_vcs
[May 25th 2010]

TORTOISESVN

Diff

1. Select Settings from Explorer's TortoiseSVN submenu.
2. Switch to the Diff Viewer tab.
3. Change the radio buttons from TortoiseMerge to External.
4. In the path edits, enter:
   "C:\Program Files\Beyond Compare 3\BComp.exe" %base %mine /title1=%bname /title2=%yname /leftreadonly

To use Beyond Compare for image comparisons either replace the file C:\Program Files\TortoiseSVN\bin\TortoiseIDiff.exe with a copy of BComp.exe, or click the Advanced button on theDiff Viewer tab and add each image type's extension with the same command line as above.

3-Way Merge (v3 Pro)

1. Select Settings from Explorer's TortoisSVN submenu.
2. Switch to the Merge Tool tab.
3. Change the radio buttons from TortoiseMerge to External.
4. In the path edits, enter:
   "C:\Program Files\Beyond Compare 3\BComp.exe" %mine %theirs %base %merged /title1=%yname /title2=%tname /title3=%bname /title4=%mname

2-Way Merge (v3 Std, v2)

Use the same steps as above, but use the command line:
"C:\Program Files\Beyond Compare 3\BComp.exe" %mine %theirs /savetarget=%merged

Here are some screenshots of the UI, from the Start button or Context menu, then the settings screen for diff and merge