If you were using Unix or Linux, you could just use the 'du' command. If you wanted to get fancy you could do something like this...
du -k | sort -nr | more
This would show the disk usage of each subdirectory, sort it numerically for you in reverse order (i.e., large directories first), and then display the results a page at a time. If you wanted just the top 10 biggest directories...
du -k | sort -nr | head -10
Yeah, there will be weenies out there who will say, "but that's so hard". At least it's possible. There are also graphical tools to do essentially the same thing like "agedu", "gdmap", or "ncdu" among others.
So an answer could be to boot up a Linux Live CD, mount the Windows drive, and the perform the instructions zeugma listed.