The BEAUti & The BEAST software package
Bayesian Evolutionary Analysis Utility (BEAUti)
BEAUti is a graphical user-interface (GUI) application for generating BEAST XML files.
It is distributed in the same package as BEAST. To download it, go to the BEAST download page.
Run BEAUti by double-clicking on the BEAUti icon in the package you downloaded.
See here for a guide to using BEAUti to create BEAST input XML.