All that you need to do is take the variables from the forumhome template and cut and paste basically. You open your forumhome template, find the stats section, and move it to the header.
I would post full instructions here, but for what has been done here, it requires a small bit of code hacking (of index.php). If you will look at vBulletin.org and find FireFly's hack that allows you to move the number of members online to the header, you will find out how I did this as well.
I would release it but there is no sense in releasing basically the same hack twice

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