[nerbert]

I don't have vB 5 but I looked at the site posted and it has

.navtabs {
            text-align: center;
}

in additional.css. See what that does.

You may need this too;

.navtabs li {
                display: inline-block;
                float: none;
}

EDIT: I'm at a disadvantage here because I don't use vB 5 so I'm doing a little guessing here. If the above CSS messes up something else try the same css but for navbar and navbar li

--------------- Added [DATE]1421368787[/DATE] at [TIME]1421368787[/TIME] ---------------

That's not a vB 5 site, it's vB 4.2.1!

I found a vB 5 site and I think this works:

#channel-tabbar {
     text-align: center;
}

.h-left {
     float: none;
}

#channel-tabbar ul li {
     display: inline-block;
     float: none;
}