The speaker cabinet is an essential part of your modeling chain that is quite underrated. The purpose of this video is to show how drastic of an effect changing between different IR's can have.
I use Reaper as a DAW and Voxengo Boogex as an IR host.
Read this to learn how to do this: http://www.guitarampmodeling.com/viewtopic.php?t=2452&f=32
Free Redwirez IR: http://www.redwirez.com/bigbox.jsp#Marshall1960A-G12Ms
More free IR's: http://bedroomproducersblog.com/2010/10/01/free-sample-shootout-6-best-free-guitar-cabinet-impulse-responses/
http://www.guitarampmodeling.com/viewtopic.php?f=32&t=2631
http://www.guitarampmodeling.com/viewtopic.php?f=32&t=17676