in windows vista, how do you organize file list by file size?

Go into My Documents or Programs or whatever you are working with.

Open a folder, and then look at the icons across the top of the open folder's window. One of the choices at or near the right is Change your View (or something like that). Click on the little down-triangle next to it (More Options) and choose Details in the list that appears.

Then all the files will be listed with file name, date modified, type, and size (left to right). Click on the word "size" to arrange the files by size.