Open a terminal, and execute the following command:
1 2 3 4 5 | $ sudo apt-get install git-core gnupg flex bison gperf libsdl1.2-dev \ libesd0-dev libwxgtk2.8-dev squashfs-tools build-essential zip curl \ libncurses5-dev zlib1g-dev pngcrush schedtool libxml2 libxml2-utils \ xsltproc lzop libc6-dev schedtool g++-multilib lib32z1-dev lib32ncurses5-dev \ lib32readline-gplv2-dev gcc-multilib libswitch-perl |