Just 2 things I would like to raise as suggestions:

1. Color highlighting would be good for the "New name" collumn (use a very 'faint' saturated color)

2. The default widths of each of the 3 collumns (old name, new name,directory) should be arranged by default so that the "New name" collumn is the most impacting i.e. the "New name" collumn has the best view 1st - just like in above mock-screenshot
Related topics:
Subject: Batch rename with action list
Subject: Ideas for 'Batch rename'
Subject: Suggestion: Rename as a Batch Convert action