NOTE: Starting with 2.1 we only release a source distribution. This issue was discussed on the developer list. Using this source distribution is really easy and avoids most of the common pitfalls of the binary distribution. See further explanation.
NOTE: Cocoon 2.1.X includes all the packages required to run out of the box (included Xerces, Xalan and FOP) so you don't need to download anything else to start.
NOTE: For earlier versions of Cocoon (which did have binary distributions). Due to the incompatibilities between JDK 1.3 and JDK 1.4, you have to choose between a binary version targeted for JDK 1.2/1.3 and a version specially targeted for JDK 1.4 (Using a build targeted for one JVM on a different JVM may result in runtime errors). Now you see why a source release is easier for everyone.