If you need to change the default directory of the Google talk received files in vista then Google doesn't help you. There is a trick you can change your default my documents directory.
Follow the steps below-
1) Go to C\users\my username.
2) Then right click on documents folder.
3) Choose Properties.
4) Switch to Location tab.
5) Click on move and choose the other location where you want your gtalk received files to be.
6) Give the answer to the dialog box comes and you have done your job.