There are so many plug ins available on the web it's crazy! In order to use some of the filters made for Photoshop you will need these .DLL files installed into your Windows system file. Follow these instructions to install the MSVCRT10.DLL and PLUGIN.DLL files.
With these .DLL files you will be able to use just about every filter created for Photoshop. Filters create many different special effects like textures and depth. It's fun to play with them to see the many different things they can do.
***Update: Something that I learned while having Windows 7 until my computer was put together...these plug ins should already be on your system. Systems running with Windows XP would need these.