If I'm reading your question correctly, you don't want to install an entire theme. Just 1 icon from a theme. Don't know about Mandrake, but this works in SUSE 9.1 GUI.
In Konqueror, right click the folder whose icon you want to change. A menu appears and at the bottom, left click "Properties". The Properties for "FOLDER" wizard appears, opened in GENERAL. In the upper left hand corner you will see the current icon. If it is enclosed in a box with a white background, then you can change the icon. If it is not, you are SOL. I haven't figured out the rhyme or reason why it allows some but not others to be changed. Left click the current icon and the "SELECT ICON" wizard appears. Left click the "Other icons" radio button and the "Browse" tab becomes activated. After clicking "Browse" you must navigate to the file that contains the icon you wish to use. After clicking that file, click "OK". The "Properties" wizard reappears and you then click "OK". The new icon will be applied.
Hope this helps.