There's two way of doing it.
First is like what you guys mentioned:-
Code:
<meta name="description" content="$foruminfo[description]" >
Change:
Code:
$foruminfo[description]
To whatever xxx you feel like replacing
Second:
Login to your admincp> Languages and Phrases> Search in Phrases
"x_powered_by_vbulletin"
Then hit edit: Saw that? Just simply replace "x_powered_by_vbulletin" with whatever xxx you feel like replacing.