Steps to use Sublime Text 2 as a merge tool (I did this on my box at work [a windows machine, sadly])

subl_git_merge.sh

  
  # first, add "sublime dir" to the PATH:
  export SUBL_HOME=/c/dev/tools/sublimetext2
  export PATH=$SUBL_HOME:$PATH
  
  # second, add a softlink to "subl"
  cd $SUBL_HOME
  ln -s sublime_text.exe subl
    
  # thrid, conf "subl" as your merge tool
  git config --global mergetool.sublime.cmd "subl -w \$MERGED"
  git config --global mergetool.sublime.trustExitCode false
  git config --global merge.tool sublime
  
  # finally, run the merge to make sure what we just did worked 
  # -- should fire up sublime text
  git mergetool -y