hi there =)
installer for win is available at : http://www.iris2.de/releases/Iris2_Setup.exe
if you're on linux you'll have to compile yourself, we don't have binaries for that yet.
iris1 is available from the svn at berlios.de, see http://www.iris2.de/index.php/Download_Iris1 for details , but i think you're better of with iris2
you'll also have to install at least a trial version of uo with 3d models as we load data from that (character models, gui),
mondains legacy trial works quite well and is available for free : http://www.uo.com/uoml/downloads.shtml
you cannot use iris to play on the original servers, they are not free of charge and have encryption, but there are a number of freeshards available.