this site as good collection of google talk themes

http://www.sapiensbryan.com/google-talk-themes/

Here goes the tutorial :-

   * 1. You will need a Resource Editor/Viewer. Download anyone according to your preference.
   * 2. Open the original googletalk.exe, which usually resides in C:Program FilesGoogleGoogle Talk folder.
   * 3. Duplicate the original googletalk.exe, just in case you might screw up editing the file.
   * 4. Open the duplicated copy of googletalk.exe using the Resource Editor.
   * 5. Expand the Bitmap tree and save bitmaps 139, 5001-5104, and 6007 (these are the files you need to edit the colour).
   * 6. Edit these bitmaps files, different bitmaps represent different portion of Google Talk interface.
   * 7. After editing to your desired colour, replace the original bitmaps with the edited ones.
   * 8. Save it and enjoy. :)

Real nice..
thanks Sankar.. :)