For those who don't know what is Pidgin can check here. For other here is tutorial how to set Gmail account on Pidgin.

1. Download & Install the latest version of Pidgin.
2. Open Pidgin and go to Add / Edit Account window of Pidgin.
3. From the drop-down box choose XMPP as the Protocol.
4. For the Screen name enter your Google Id (Gmail Id). eg. bossalifaan
5. For Domain enter gmail.com

6. You can leave the Resource with the default "Home".
7. In the Password field enter your Google ID password.
8. Enter Local alias as whatever you want to.

Now u can chat whit your Gmail friends using Pidgin, Enjoy.