A 32-bit Linux binary can be downloaded from the JD-GUI homepage. The tar.gz file just contains a single binary executable. I installed it as follows:
Since my box is 64-bit, I was missing a handful of 32-bit libraries on which JD-GUI depended. Fortunately, these were all available from the default Fedora yum repos and can be installed using the following command:
tar -xzvf jd-gui-0.3.3.linux.i686.tar.gz sudo mv jd-gui /usr/local/bin
These are the packages for Fedora 12 or later. If you're on Fedora 11, suffix the package names with .i586, rather than .i686. For Fedora 10, use .i386 as the suffix.
sudo yum install libcanberra-gtk2.i686 PackageKit-gtk-module.i686 gtk2-engines.i686
If you're using GNOME as your desktop environment, you may also want to associate .class files with JD-GUI. To do so, open File Browser and find a .class file. Right-click on the class file and select Properties. Select the Open With tab, click the Add button, select "Use a custom command", enter "/usr/local/bin/jd-gui", and finally click the Add button. Now when you double-click on a .class file from the File Browser, it will open that file using JD-GUI.