The Spitzer Observer's Manual Chapter 7 of this manual describes the IRS and how to use it. This chapter is a must-read for anyone wishing to apply for IRS time.
SMART - Release Information about and access to the IRS Spectroscopy Modeling, Analysis, and Reduction Tool. Released as free (GPL) software to the worldwide astronomical community.
CAFE - SED Decomposition Software Information on the CAFE software package written by Jason Marshall to decompose the SEDs of dusty sources.