I am attaching a sample file, MinimalExample.tex, containing only one verse, for newcomers to experiment with.  To typeset it one needs to have previously downloaded all of the packages listed in the first several lines: ledmac, fancyhdr, xunicode, and SDVerseMG.sty.  The last was kindly made available by Somadeva Vasudeva in order to easily reference variants in the critical apparatus by verse number and pāda, rather than just line number.
One further procedure is necessary to have the convenience of typing the source file as unicode roman, and having the typeset version come out in Devanagari.  For this you need to install TECkit, available from SIL International.  Once you have TECKit, go to Dominik Wujastyk’s blog “Cikitsa” and see this entry.  Some of the links are now dead, but one from Somadeva Vasudeva’s blog “Sarasvatam.blogspot.com” is here.  Following his instructions, I hope you will be able to successfully compile the sample file.
I should also say that this is meant to work on a Mac, using the Apple font DevanagariMT.  In theory one should be able to use it on any system and simply substitute another unicode devanāgari font.  I welcome questions and comments, and I’ll revise the instructions if I have omitted any steps.