Unable to save hosts file after adding websites to block.
This specific request "I want to block sites and need to edit /private/etc/hosts" requires you to know how to edit a normally hidden system configuration file. Your information on an older processor and OS are excellent, but in this case all OS X work the same for modifying the unix host file.

This error is intentional and by design, since making this file easy to modify means that you could easily break the computer from working (and also this file is very desirable for malware or trojan/virus software to attack - imagine if your banking website was directed to another site to harvest your user and password before sending that information to your real bank as part of a "man in the middle" attack.)

Most people use a terminal based editor since it's easily to use the sudo command to temporarily edit the file with root permissions - taking care not to undo the protections that make this not writable by any users directly.


Mac OS X Server: How to edit configuration files


As always, be sure you know how to correct a change like this - the normal Time Machine backup should preserve this file if you know how to to navigate to the /private/etc folder using Finder Go -> Go to Folder... keyboard shortcut before entering Time Machine.