Firstly, Here is the website to get a chatbox for your blog :
http://www.cbox.ws/ And register for a account, And then click Create my Chatbox
But firstly on the homepage Click get your own free Chatbox Now !
Then register, Log in , Press The Publish word on your top right, and then copy the code from the clipboard, And follow the steps below.
The steps are shown below , Just follow it and you will get you chatbox on your lovely blog :
1. Copy your code to the clipboard by clicking the button above.
2. Sign in at blogger.com / blogspot.com.
3. On your blog, go to the dashboard by clicking "customize".
4. Click on "Layout"
5. Select "Page elements".
6. Click "Add a Gadget".
7. Choose "HTML/JavaScript", click the content box and paste your code in it by pressing Ctrl+V.
8. Save the changes.
Are you done? Congratulations !!