Acronym System or Plugin?

[kh99]

It's really just an html <abbr> tag, so you could make a test html file with one in there and see what it looks like, or just add the bbcode and try it in a test post, and remove it if you don't like it. You can also add CSS to your additional.css file to change with it looks like.

Actually, here's another one that does pretty much the same thing but has scrren shots and shows the CSS to modify how it looks: www.vbulletin.org/forum/showthread.php?t=273008 .

One limitation of both of those is that the popup can only contain plain text. If you wanted an html popup window, you'll have to use something more complex (like something javascript-based).