Google now provides a useful badge for developers to incorporate easy chat interface with the site visitors by showing site administrators Gtalk status on webpage and up on clicking poping up chat interface
Steps to incorporate this to your website
(assuming you are signed in to google account)
A Google Talk chatback badge will let visitors to your web page chat with you. They’ll be able to chat with you whenever you’re signed in to Google Talk as email@example.com. For more information, visit the help center.
Each time you visit this page, we generate a new badge for you so you can use badges with different settings on different web pages. For example, you can share your status message on your personal blog and not on your public blog. To change a badge later, just return to this page and get a new one.
2.click on the edit button to change your details
To use this badge, copy and paste the HTML code below into your web page. If the site that hosts your web page does not support direct HTML editing or embedded frames then click ‘Edit’ to select a style of badge that does not use frames. If you want to include your badge in an email message, you should use the ‘Hyperlink only’ or ‘Url only’ styles.
the badge style can be edited, the default badge looks like