This should install two commands: node and npm.

npm may require some extra configuration to set permissions properly on your system.

On Mac OS X, do the following:

npm config set prefix ~/.npm
echo 'export PATH="$PATH:~/.npm/bin"' >> ~/.bashrc

On Windows, fire up Git Bash and type the following:

mkdir /c/Users/$USER/AppData/Roaming/npm
echo 'export PATH="$PATH:/c/Program Files/nodejs"' >> ~/.bashrc

Note: if you installed the 32-bit Windows version of node, the second line above should instead read:

echo 'export PATH="$PATH:/c/Program Files (x86)/nodejs"' >> ~/.bashrc