Hi,
Firstly, if u use file roller, open the tar.gz file again and u will see the top text box. There's the place where u have installed.
To do a lookup efficiently, do the following:
1. Type "updatedb" in ur new terminal.
(Terminal ---> right click on the desktop and choose "Open Terminal")
2. Wait for a couple of minutes.
3. Once finish, type "locate xxx" (xxx is the file name for xxx.tar.gz u have unzipped)
Lastly, always try to put ur tar.gz files in /home directory. U will not be lost. Also, always u make sure that u extract at the home directory in the first place.