I modify it a bit so it works on MacOS X.
First, you need to install meld from homebrew.
Then create a shell script "svn-diff-meld" in ~/bin:
#!/bin/sh
# SVN Diff Wrapper for Meld
# KOG 2008-02
# This line is only need if you use it on MacOS, assuming meld installed by homebrew
export PYTHONPATH=/usr/local/lib/python2.7/site-packages
left="$6"
right="$7"
meld "$left" "$right"
add alais to do svn diff w/ meld:
alias svn-diff='svn diff --diff-cmd=/Users/me/bin/svn-diff-meld'