Thanks @JonAniano.

In my Customer Portal setup, I've used this code (literally, what you see is the entire text). It's saved to a text file that I've named as "footer.txt", saved into the Documents folder, and associated with  the "Footer" field of the "Look and Feel" section of the Customer Portal.

(Note: there are no files or any lookups associated with the Header field in the "Look & Feel" section)

<h2>This is a title before the footer</h2>
<p></p>

<!-- START Salesforce Live Agent Button/Link Code: Place this code into your HTML wherever you want this button/link to appear -->
<script type="text/javascript">
var __ALC_BADGE_SUFFIX = (Math.round(Math.random()*10000000000));
document.write('<div id="__ALC_BADGE_ONLINE'+__ALC_BADGE_SUFFIX+'" style="display: none;"><a href="javascript&colon;//chat" onclick="_alc.startChat(15120); return false;"><img id="__ALC_BADGE_ONLINE_IMAGE" style="border: 0px none" src="'+unescape(document.location.protocol+'//depot.liveagentforsalesforce.com/app/chat/buttons/55/btn2_blu2_3.gif')+'" /></a></div><div id="__ALC_BADGE_OFFLINE'+__ALC_BADGE_SUFFIX+'" style="display: none;"><img id="__ALC_BADGE_OFFLINE_IMAGE" style="border: 0px none" src="'+unescape(document.location.protocol+'//depot.liveagentforsalesforce.com/app/chat/buttons/55/btn2_blu2_2.gif')+'" /></div>');
if ( typeof(__ALC_Badges) == 'undefined' ) __ALC_Badges = new Array();
var __ALC_BUTTON = new Object(); __ALC_BUTTON.id = '15120'; __ALC_BUTTON.available = '__ALC_BADGE_ONLINE'+__ALC_BADGE_SUFFIX; __ALC_BUTTON.unavailable = '__ALC_BADGE_OFFLINE'+__ALC_BADGE_SUFFIX; __ALC_BUTTON.department = 0; __ALC_Badges.push(__ALC_BUTTON);
</script>
<!-- END Salesforce Live Agent Button/Link Code -->

<p></p>

<!-- START Salesforce Live Agent Deployment Code: MUST BE PLACED DIRECTLY ABOVE THE CLOSING </BODY> TAG and AFTER/OUTSIDE ALL HTML -->
<script type="text/javascript">
var __ALC_Deployment = 9716;
document.write(unescape("%3Cscript src='"+document.location.protocol+"//depot.liveagentforsalesforce.com/app/js/lt.js' type='text/javascript'%3E%3C/script%3E"));
</script>
<!-- END Salesforce Live Agent Deployment Code -->

 As this is just meant for the Portal's footer, I've also considered adding just closing body & html tags after the liveagent code, too.

WDYT?