After closing gtalk, it is not really closed. It goes to system tray. So I need to exit it again. I want it to be completely closed after I click the cross sing of gtalk. How should I do?

That would be the design of Gtalk and have nothing to do with windows 7. Search for a setting in gtalk that closes on exit.

Thz. I will try :)

There are no options to disable "hide to system tray" like some other applications. I close it by just right-clicking on the gTalk icon on the system tray and Exit. And as defcon says, that is a setting related to the application, not Windows. There may be a registry setting that could change that though. If you do find a solution to closing it in that manner, i'm curious and let us know!