I found this in a few different places around the 'net - hopefully it's helpful:
How to Change the Default Icons for Folders in Windows XP
You cannot customize the default icon for a folder in Windows; however, you can make a shortcut to a folder and change the look of the shortcut icon. To make a shortcut to a folder and change the look of the shortcut icon:
- Open My Computer and browse to the folder that you want.
- Right-click the folder, and then click Create Shortcut. If you are prompted to place the shortcut on the desktop, click Yes.
- Right-click the shortcut you created, click Properties, and then click Change Icon.
- Click the picture of the icon you would like the shortcut to use, click OK, and then click OK.
No Icons Available
If you click Change Icon, and there are no icons available, use the Browse button to find Shell32.dll:
- Right-click the shortcut you created, click Properties, and then click Change Icon.
- Click Browse, type %systemroot%\system32\shell32.dll in the File name box, click Open, click the icon you want to use, click OK, and then click OK.