The latest version of 188.8.131.52 has been released recently but RIM left out the preloaded wallpapers. I realize that many people, including myself, usually go out of their way to remove these but lots of folks actually like them. So, if you're one of those people who just has to have the preloaded wallpapers OR the custom folder icons, here they are. They are simple alx/cod type installation file and Desktop Manager is required to load them.
Simply unzip the files into a folder somewhere you won't delete them. Then use the "Add" or "Browse" feature in Application Loader and browse to the .alx file. It should add the medialoader.cod to the application loader. Click on Finish to load the files to the BB. After the file has been installed, disconnect from the PC and remove the battery from the device to reboot.
320x240 for 83xx, 88xx, 8700 devices
240x260 for 81xx devices