For Linux there is no installer. Just untar the file and cd in the directory and type ./Foldit or double click on the Foldit icon in the Foldit folder (within a long list of files).
If nothing happens or if you get an error like "Foldit Error: Could not load library: libglut.so.3: cannot open shared object file: No such file or directory" you need to install the "freeglut3" package. In Ubuntu you can install it via the Software Center or the Synaptic Package Manager, or typing the following in a terminal: "sudo apt-get install freeglut3". The Fedora package name is "freeglut". You may also need to install "libnss-mdns".
There is a possibility that on first login the user name can not be entered. Clicking on the check boxes will show the user name box!
For Linus 32 bits : You can use WINE and run windows 32bit version under linux.
How to add a Linux Desktop Launcher