unable to install npm packages in node.js

i am beginner for Node.js , i try to install some packages like express.js, underscore.js using Node.js by NPM but every time im trying to install using following command:

npm install express,

npm install underscore

Its showing error. please Refer following image,. please help me to fix this. how to install packages in npm by node.js

Please refer image here

Thanks in Advance...

via Sivakumar Munusamy