Here is my attempt at doing it. I haven't tested extensively, but it seems to work (with two books, two inline citations, and two footnote citations with dummy footnotes in-between).
The idea, following what Paul Stanley said in his comments, is to use BibLaTeX to index things properly. In order to do so, we need to redefine \DeclareIndexFieldFormat (which is used for indexing titles, but it has several variants for names, etc.), and to create a macro that will format the page number by appending the footnote number to it.
I am also renewing two macros because biblatex does some formatting before indexing titles, and we need to preserve it while incorporating the added |note command.
\documentclass{memoir}
\usepackage[backend=biber,indexing=cite]{biblatex}
\makeatletter
\DeclareIndexFieldFormat{indextitle}{%
\iffootnote%
{\usebibmacro{index:title}{\index}{#1}{|note{\thefootnote}}}%
{\usebibmacro{index:title}{\index}{#1}{}}%
}
\renewbibmacro*{index:title}[3]{%
\usebibmacro{index:field}{#1}{\thefield{indexsorttitle}}{\emph{#2}}{#3}}
\renewbibmacro*{index:field}[4]{%
\begingroup
\protected@edef\theindexentry{%
\unexpanded{#1}{#2\actualoperator\unexpanded{#3#4}}}%
\theindexentry
\endgroup}
\newcommand{\note}[2]{#2n#1}
\makeatother
\begin{filecontents}{\jobname.bib}
@book{author:2000,
author = {Author, A.},
year = {2000},
title = {My first title},
}
@book{buthor:2002,
author = {Buthor, B.},
year = {2002},
title = {My second title},
}
\end{filecontents}
\makeindex
\begin{document}
Some inline citation \cite{author:2000}. Some footnote\footnote{A, b and c}. Some footnote citation \footcite{buthor:2002}.
\clearpage
Some footnote\footnote{A, b and c}. Some footnote citation \footcite{author:2000}. Some inline citation \cite{buthor:2002}.
\printindex
\end{document}
Edit: Looking at your first question, I think perhaps you could create an entry using the following code:
@book{digest,
title = {Digestum},
indextitle = {Digestum!\emph{Dig.}},
indexsorttitle = {02},
}
@book{institutes,
title = {Institutiones},
indextitle = {Institutiones!\emph{Inst.}},
indexsorttitle = {01},
}
Don't forget to replace the \emph{#2} by #2 in \renewbibmacro{index:title} at l. 14, otherwise it won't work.
Now, if you want two indexes with one of them being sorted arbitrarily and the other alphabetically, you need to specify things accordingly, by saying where to index which data (see the memoir documentation). If you further want the "Institutiones" and "Digestum" to look like letter headings, I suggest you look for a way to solve your first question with xindy (or wait until someone find it). Sorry I can't help there.
indexing=cite) does not indicate whether the citation is in a footnote or not. – jon May 11 '12 at 21:11.idxfile (which biblatex would need to write to) so you get as the last argument to an index entry something like{3n1}(i.e., the page reference), then runmakeindexon the.idxfile, it will skip those entries when it creates the.indfile, which *latex uses to create the index. – jon May 11 '12 at 21:42