Sorry Michael, I fed you a slightly inacurrate piece of information. You do have an icon cache like I stated before, but it has been renamed and relocated under Windows XP (as opposed to earlier versions of Windows). This file is a "database" of the icons that Windows has opened from various files throughout your system. This gives Windows a quick way to refer to icons without having to open every file on the system every time it needs to display them. Instead, it just goes to this cache. But sometimes the cache file can get corrupted (TweakUI from Microsoft has been known to cause this for some people).
Try this better and updated info:
1. Go to "Start | All Programs | Accessories | Windows Explorer".
2. In Windows Explorer pull down the "Tools" dropdown menu and select "Folder Options". This will open the "Folder Options" dialog box.
3. Select the "View" tab.
4. Scroll through the "Advanced Settings" scroll box and locate the item called "Show Hidden Files and Folders" and mark it active.
5. Scroll through the "Advanced Settings" scroll box again and locate the item called "Hide Extensions for Known Filetypes" and mark it active.
6. Click "OK" to close the "Folder Options" dialog box. This will return you to your Windows Explorer application.
7. In the left pane of Windows Explorer open the "My Computer" sub-tree and drill down through this directory structure (substitute whatever is appropriate on your system where mine indicates "bob" below):
c:\documents and settings\bob\local settings\application data\
8. Within the folder described in step 7 you should find the file called "IconCache.db". You can rename or delete this file. Windows will recreate it when you reboot.
9. Reboot.
Many times if this file is recreated it will get rid of the blackened icons. This has worked for me a few times.