Folders question

I would like to know this too

 

To change the icon for any disk, app, file or folder

To change the icon for any disk, app, file or folder:

1. Copy the image you want to use (use Command-C to copy):
   • If copying from an .icns file, double-click to open in Preview, Command-A to select all and Command-C to copy.
   • If copying an icon used by another file, folder, app or disk, right-click and Get Info on that item, click the icon in the upper left, then copy.
   • If copying from a picture, double-click to open the pic in Preview, then Command-A to select all of the image and Command-C to copy.
2. In Finder, locate the item you want to change
3. Right-click and "Get Info" (or Command-I)
4. Click the icon in the upper left corner of the Get Info window
5. Command-V to paste

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To revert back to the original icon, simply click on the custom icon and press Delete.

Mac 101: Change your icons

 

I don't think that's what the OP was asking. Windows XP will put small thumbnails in the folder icon itself of the pictures contained within the folder.

AFAIK there isn't a way to do this in OS X, certainly not out of the box.