Our client wanted to integrate mailchimp with magento. So I dig for extension and found this awesome free magento extension called mageMonkey. I installed it through magento connect using key: http://connect20.magentocommerce.com/community/Ebizmarts_MageMonkey
Today's task for me was to connect existing site's newsletter subscription to mailchimp using mailchimp's API. So, after going through some API docs on mailchimp, this is what worked for me. So, this is my log for short and direct steps and links for next time when i have to work with mailchimp again. Hopefully it will help someone else too.