On Ubuntu, as root, install the nodejs and npm package via apt-get
# apt-get install nodejs npm
Alternatively download and unpack in /opt. After this users should add it to their PATH.
Download the Windows Installer and install everything.
Individual users can install packages into their home directories.
e.g. to install bower module, run
$ npm install bower
To find out where the binary is installed run
$ npm bin
Add this directory to your PATH.
To workaround this, clear the cache and try again
$ npm cache clear
bower is a package manager you can use a web project.
Run bower init in your project directory. A bower.json file will be created that describes the project and dependencies. Next you can add dependencies such as Polymer
bower install --save Polymer/polymer
When you run this, dependencies are downloaded to the directory bower_components. The bower.json will be updated with the new dependency.
The bower_components should be marked as ignored in version control and should not be checked in.
grunt is a build tool.
Using npm, install grunt