I found this in a few different places around the 'net - hopefully it's helpful:

Add Fields to the Details View of Folders

You can add other columns to the Details view of the files contained in Windows XP folders, such as Comments, Description, Category, and many others. To add new columns:

• Right-click the column header of the files list, and then click one of the fields listed, or click More.
• In the Choose Details dialog box, you can reorganize the order of column headers, specify column widths, and add columns to display details for the files in that folder.

When you click the new column header, the width of the selected column is displayed in pixels in the Choose Details dialog box.