Unzip the example design, synthesize it, and then read the scripts to see how things work. You'll see that there is a constraints file implemented in Tcl. Learn how to use Tcl and constraints applied like this.
The DE4 comes in a couple of varieties, eg., a 230k and 530k version. I forget which board I have ... most likely whatever the script defaults to :)
Using Tcl scripts for managing constraints is quite universal - with very minor changes the constraints style works for Xilinx Vivado too.
Cheers,
Dave
