Are you using FrostWire or LimeWire? The skin installer is specific to which program you are using. The FrostWire Skin Installer will not work for LimeWire (& vice-versa) because the FW & LW skins each use a different file extension. LW will not recognise FW skins, & FW will not recognise LW skins.
All your previous posts on the forum refer to using LimeWire.

Oops I just realised I think File_Girl inadvertently replaced the original LW skin installer download-link with the FW one. I'll let her know. A simple mistake musicmad. This is the original link LimeWire Skin Installer.

Edit: File_Girl has now fixed the download link in her first post.

BTW I tested the LW skin installer using Windows 7 & 2000, & using LW 4.16.7 & it all worked well.

Will the skins be compatible with the earliest versions of LW 4, I am not sure. There were some interface changes in LW 4. It's my guess some skins may not work with 4.8 & earlier (the junk filter was introduced in LW 4.9 & some other minor interface changes such as priority setting.) Probably LW 4.0 would be the most at risk but I doubt anybody is using the 4.0.x versions any more on Windows, it's quite out of date for abilities. At a guess, probably any version of LW from 4.12 or higher most if not all of the skins will all work.