When you're on Limewire, you click on View - get more skins. When the page opens up, click on a skin you like. It will open up in a box to open or save, but it will come up like this: party_theme.zip (or whatever one you pick).
All you do is 'Save' the file. Then open up your 'My Computer' icon, then click on 'Local Disc C, Documents and Settings, Client (or whatever you have typed there for you), Application Data, Lime Wire, themes. Your theme will be there but will be a .zip file. Just delete the .zip part and type .lwtp instead. It will tell you if you delete that, some files might not work, but do it anyway. It changes the .zip file to a regular file. Then, make sure Limewire is totally exited, re-open it again, click on 'View', 'apply skins', and your new skin should be there. Hope you understood all this.