The FX-Foundry Scriptpack is a collection of over 100 really useful scripts for GIMP 2.6 and later. Admittedly the scripts have not been maintained recently and some no longer work, however they are still an amazing resource. The following instructions explain how to install the FX-Foundry scripts on Linux.
1. Download the Scripts
Go to the Sourceforge page to download the latest tar.gz archive of the scripts - http://sourceforge.net/projects/gimpfx-foundry/
2. Unpack the archive
Change directory to your GIMP scripts folder. This will be located in your home folder under .gimp-2.6 or .gimp-2.8
cd ~/.gimp-2.8/scripts
Once there, unpack the archive. Assuming you downloaded the archive to ~/Downloads:
tar xzvf ~/Downloads/gimpfx-foundry-scriptpack-20080323.tar.gz
This will extract a number of files into your current location.
3. Restart GIMP
If you had GIMP running when you did this, you will need to restart. If not, just fire her up. You should now have a new a new menu item at the top of the main GIMP window called "FX-Foundry". The scripts can also be found in your right click context menu, again under "FX-Foundry". Have fun!