\footnotemark to signify the repeats:
...\footnote{Repeating note}
...
...\footnotemark[1]
… which is very easy, since we know there will only ever be a footnote number 1. A similar technique can be used once the footnotes are stable, reusing the number that LaTeX has allocated. This can be tiresome, though, as any change of typesetting could change the relationships of footnote and repeat: labelling is inevitably better.
Simple hand-labelling of footnotes is possible, using a counter dedicated to the job:
\newcounter{fnnumber}
...
...\footnote{Text to repeat}%
\setcounter{fnnumber}{\thefootnote}%
...
...\footnotemark[\thefnnumber]
but this is somewhat tedious. LaTeX’s labelling mechanism can be
summoned to our aid, but there are ugly error messages before the
\ref is resolved on a second run through LaTeX:
...\footnote{Text to repeat\label{fn:repeat}}
...
...\footnotemark[\ref{fn:repeat}]
Alternatively, one may use the \footref command, which has the
advantage of working even when the footnote mark isn’t expressed as a
number. The command is defined in the footmisc package and
in the memoir class (at least); \footref reduces the above
example to:
...\footnote{Text to repeat\label{fn:repeat}}
...
...\footref{fn:repeat}
This is the cleanest simple way of doing the job. Note that the
\label command must be inside the argument of
\footnote.
\DeclareFixedFoot command, and
then use the command you’ve ‘declared’ in the body of the document:
\DeclareFixedFootnote{\rep}{Text to repeat}
...
...\rep{}
...\rep{}
The package ensures that the repeated text appears at most once per page: it will usually take more than one run of LaTeX to get rid of the repeats.
This question on the Web: http://www.tex.ac.uk/cgi-bin/texfaq2html?label=repfootnote