I'm curious, though, if you can use HTML code/vB Code in the descriptions.
Yes, you can use HTML...all HTML will be stripped from the Random Term JavaScript display, though. No, right now it doesn't parse for vB Code, but if you want, I could upload a modified glossary.php file and have it do so. It's a VERY minor change, really.
And is there a way that you can link one glossary entry to another (or several others)?
Well, sort of. You can display only a specific term. Like this (I forgot to add error-checking for it, though, I think):
http://www.movieforums.net/glossary.php?glossaryid=48
So, in that sense, you can link to a term directly. I dunno what you mean about several, though. You mean have "related terms" or something?