This project has been taken up in the official codebase of TikZ and pgfplots in a much improved manner (thanks to Stefan Pinnow). It is highly recommended to use that library, rather than the version hosted here.
Simply put the files in a directory where LaTeX can find your files. On linux,
for example, put these files in
~/texmf/tex/latex/colorbrewer/ (you might have
to create the directory). Then run
texhash to update the definitions.
There are two example files
which illustrate the usage. The second example outputs a list of all colours.