Some people say that if you just put the folder (for example, Matrix) in a folder named "skins" on the C drive it'll detect.
I have a file in my C drive, you can make called "MXM.xml". You can edit it in notepad and put the following text.
Now create a folder in the C drive called "Skins". Then put in the folder containing the skin yopu want in the folder. For example, the folder "Matrix" contains an Skin.xml file and some wma files, etc...
then reboot..and that should do it