Microsoft Operating systems don't provide a conveinent mechanism for discovering folder (directory) sizes (even in windows 7). They do however provide a downloadable utility called du, which coupled with a simple for statement, can provide the necessary info.
List directory sizes.
Disk Usage
Download Du zip and unzip to your documents directory
Open a command prompt->cd C:\Documents and Settings\MarkN\My Documents -> or directory you unzipped to.
Cut and paste following to a command prompt, update red colored directory name to desired value
for /D %f in ("
C:\users\*") do du -q -v "%f" | find "Size:"