The need for more than one series of footnotes is common in critical editions (and other literary criticism), but occasionally arises in other areas.
Of course, the canonical critical edition macros, edmac, offer the facility, as does its LaTeX port, the ledmac package.
Multiple ranges of footnotes are offered to LaTeX users by the manyfoot package. The package provides a fair array of presentation options, as well. The (rather new) critical editions ednotes package is built upon a basis that includes manyfoot, as its mechanism for multiple sets of footnotes.
This question on the Web: http://www.tex.ac.uk/cgi-bin/texfaq2html?label=multfoot