This tar ball contains two sets of hydroxyproline parameters. The more recent set of parameters was developed in 2005. See Park et al (J Comput Chem. 2005 Nov 30;26(15):1612-6) for details. The two relevant files are prepHYP05.in and HYP05.forcemod. They are the amber prep file and some additional parameters you will need to add to the parameter file (note that we had to make a new atom type, 'OO', which uses many of the older 'OH' atom type parameters).