This package was originally created by Stephane Champely, from the University of Lyon.
The official release of the package is on CRAN: http://cran.r-project.org/web/packages/pwr/
To get it installed, just write in an R session:
install.packages("pwr", repos="http://cran.r-project.org")
To work with the newest development version, check the build status icon at the top of this page. If it says "passing", you should be able to install it from the source. Clone this Git repository in your machine, and if you have the tools to build R packages, do it and install it as appropriate for your OS.
If you cannot build it, you may still install it from an R session (at the expense of not having PDF docs). Set the working directory to the parent folder where pwr is copied, and then do:
install.packages("pwr", repos=NULL, type="source")
After installing, you have to load to use the package, with:
library(pwr)Feel free to comment on any issues, file bugs or suggest improvements. All contributions are welcome!