It doesn't explicitly need to be Windows. I'll try and get hold of a linux box and take a look at du. (At the moment I have a choice of Win2000 or Solaris, and the former I'd never really considered using perl, since I have the latter)

I'd largely rejected du, primarily because in it's POSIX form it just prints the current level. (so in order to show sizes at each of the levels, you're effectively doing the job 5 times).