Thank you, you pointed me in the right direction.
But now I've encountered another problem.
This is tricky to explain... at the bottom of the page is the "Currently Active Users" section. It currently displays usernames, which I don't want, I want the Display Name ($bbuserinfo[field5]). Now, the forumhome_loggedinuser template has the code for that section, and vB uses the $loggedin[musername] variable. I'm wondering how to make the $loggedin[musername] return Display Names, not usernames.
I'm guessing I'm going to have to go in and edit the function itself.
Where would I find that function?