I found the problem, me thinks............ the UIS files reads this way....
[TitlebarSkin]
SkinName=Niobium
SkinAuthor=Bones2112
AuthorEmail=bones2112@skinartistry.com
SpecialNotes=
AuthorsURL=www.skinartistry.com
Generator=Stardock SkinStudio Professional ver 4.0.0, Build 831 - http://www.skinstudio.net
WBVer=400
EditorNotes=Made for the 2004 GUI Olympics
[XPShell]
File=NiobiumBlue\ShellStyle.xps
[Animations]
File=NiobiumBlue\Luna.Animations
[ToolbarIcons]
File=NiobiumBlue\Luna.ToolbarIcons
[XPTaskbar]
File=NiobiumBlue\Niobium_xpstuff.xp
[Personality]
BUTTONCOUNT=39
ColourAware=0
Top=NiobiumBlue\NiobiumBlueWindowFrameTopUis2.bmp
Left=NiobiumBlue\NiobiumBlueWindowFrameLeftUis2.bmp
Right=NiobiumBlue\NiobiumBlueWindowFrameRightUis2.bmp
Bottom=NiobiumBlue\NiobiumBlueWindowFrameBottomUis2.bmp
The skin name is Noibium, so that's the folder that is created upon installation.... but all the file are pointing to a NoibiumBlue folder, which doesn't exist on anyones computer other than yours.
So, it works for you, but can't find the images for anyone else.
Simple fix is rename the skin in the UIS, to NiobiumBlue. 
Now that I think about it, you can't just rename the skin in the UIS, but it will have to be saved as such.......
(this stuff always confuses me), and now that you see the problem I'm sure you'll figure it out.
[Message Edited]