I think it depends on your operating system but try:
C:\Users\*your username\App data\local and have a rummage in the sub folders (some of my I-Poker skins are stored here)
Also, make sure you folders aren't hidden. To unhide follow this (C/P from a search):
Access the Control Panel. ...
Type "folder" into the search bar and select Show hidden files and folders.
Then, click on the View tab at the top of the window.
Under Advanced Settings, locate "Hidden files and folders." ...
Click on OK.
Hidden files will now be shown when performing searches in Windows Explorer.
Hope that helps