Reminds me of a little utility I used to use a lot "Treesize". The page at link below says "TreeSize Free is freeware for Windows 2000/XP/Vista/7. Users of Windows 9x/ME can download the last compatible version TreeSize Free V2.1."
The rather old free version I used on XP works only on local drive - can't use it to check network drives. (I never did try the paid version. Nor have I gotten around to putting on my year-old Vista - kinda forgot about it!!) I thought it was rather a neat program.