Web Messengers ? In Which Programming Lang They Are Done ? Can any one help me in creating a web messenger ?

Today we know and we have come across a lots of web messengers. Web messengers are something which serves the purpose which the normal messengers like yahoo , google , rediff, aol etc. serves. Using the normal messanger one can have a chat etc. The Webmessengers too provides you the same facility but some services are limited. So talking about the web messengers , they can be broadly classified into two , one is gonna be the one which is provided the Company itself, Lets take yahoo for example . In yahoo every one is aware of the messenger they provide , the normal one which we install in our computer and we use, and on the other hand when we login to our yahoo mail account we can see something in the right corner of the mail account when logged in , thats the web messenger which yahoo provides. On the other hand we can see many other web messengers from which we can login to yahoo and use the messenger like meebo where we enter our user name and password of yahoo , and they connect us to the orginal yahoo server. Here Meebo acts like a proxy, so as all the third party webmessengers. On the other hand they have their own Privacy Policy which states that they get the informations like user name and passwords and they access .So my question here is that how to create a thirt party webmessenger for google talk so that i can host it in my website ? I do understand Google has its google gadgets which provides webmasters to attach google talk to their sites, but this is from google, im asking like meebo is there any way to create a 3rd party web messenger to my website through which users can login to google talk. If there is any open source for creating and using webmessengers please let me know, or if anyone can help me with the code with which i can create a web messenger please let me know. Thank You .