Is the original source in 5.1? If not, you're better off leaving it in 2.0 and letting your decoder do the pro-logic treatment to it. If you're mixing 5.1 and 2.0 sources, then the doom9 guide works great for upmixing your 2.0 stuff to 5.0 (sadly the .1 remains empty). Read the Vegas part of my guide for re-mixing your final result in 5.1 if you have a 5.1 source to work with. Good luck!