As a general rule, if it isn't under /home or /media, you'll need to prefix any command that needs write privileges with sudo. for example, to edit my sources.list, I type:
Code:
sudo nano /etc/apt/sources.list
Also, in my experience, the only things you need under /etc/apt are sources.list and the trusted files. Can't help much with Synaptic since I ditched it in favor of Aptitude years ago. If you posted copies of the actual terminal output instead of screenshots, I might could give specific advice. Pro tip: appending > filename to the end of a terminal command will redirect output to a text file name filename. 2> filename will redirect error messages, and >> will append output to an existing file.