Thanks very much harmor.

I realize that this is super basic and it'd be far quicker to just do the template edit - I'm just using this as a stepping stone to get a feel for the actual process. 99% of the "modding" that I do are template edits, and I'd love to be able to release some of them as products. I think if I can get this working and learn the basics, I can build off of that to make more complex/useful bits.
Where would I actually define that variable in the plugin?
Here's what I have right now, just adding in a phrase instead of the text. I'll start looking for the variable stuff from here.
Code:
<?xml version="1.0" encoding="ISO-8859-1"?>
<product productid="chris777_showinvisible" active="1">
<title>Show Invisible Users</title>
<description>Will add a count of invisible users in WGO.</description>
<version>1.0.0</version>
<codes>
</codes>
<templates>
</templates>
<plugins>
<plugin active="1">
<title>Show Invisible Users</title>
<hookname>forumhome_loggedinuser</hookname>
<phpcode><![CDATA[
if ($totalonline (<phrase 1="$numberregistered" 2="$numberguest">$vbphrase[x_members_and_y_guests]</phrase>))
{
$vbphrase[online_invisible] $numberinvisible;
}
]]>
</phpcode>
</plugin>
</plugins>
<phrases>
<phrasetype name="GLOBAL" fieldname="global">
<phrase name="online_invisible">
<![CDATA[ Invisible:
]]>
</phrase>
</phrasetype>
</phrases>
<options>
</options>
</product>
I think the most basic question I have then is, how do I go about adding what I'm looking to add directly after this text in the forumhome template?
Code:
if ($totalonline (<phrase 1="$numberregistered" 2="$numberguest">$vbphrase[x_members_and_y_guests]</phrase>))
Thanks again and I apologize for the super-basic-and-pretty-much-useless bit of code that I'm working on. I'm really looking forward to getting better at it and a couple of coders pointing me in the right direction will no doubt save me hours of API digging.