messing around with permissions

[auto]

This is not really a hack, so I won't put it in the requests forum.

My site has been eating up a lot of bandwidth as it keeps growing. Right now its over 20 gigs per month and site is not even 6 months old
I have no problem with my members eating up bandwidth, but Guests... um NO
So here's my idea:

Allow Guests to view
Forum home- http://64.21.152.50/vbulletin/index.php ,
the forum structure- e.g. http://64.21.152.50/vbulletin/forumd...s=&forumid=714 ,
and thread titles- e.g. http://64.21.152.50/vbulletin/forumd...s=&forumid=666 ,
BUT not the threads themselves- e.g. http://64.21.152.50/vbulletin/showth...&threadid=2591

How can this be accomplished?

thanks,