IF i put someone in the moderator usergroup, then will he be shown as moderator of all forums(ie every forumdisplay.php will have his name shown as moderator)? Can I specify him as a moderator of only 1 forum and at the same time set him in moderator group? I feel confused because it seems that putting someone in moderator group will grant him all moderating privilege in all forums.

The moderator usergroup is basically a label. You can make someone a moderator of a forum but have their primary group as Registered Users.

If you put someone's primary group to moderator then they will follow the rules of the moderator usergroup, in the same way that a banned user will follow the rules of the banned group. This is so you can give the moderators different options such as more private message, bigger avatars, a coloured name etc. if you like.

You have to set someone as a moderator of a particular forum for them to have power there.
And forumdisplay.php will only show moderators of that particular group. So if a user is a moderator of forum 1 but not forum 2, they will only show up as a moderator in forum 1 even if they're in the moderator usergroup.

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"When you do something right, people won't be sure you've done anything at all" - "God", Futurama

My vB hacks: Site Backup (easily backup your forum files) -- Image Status Checker / Dead Image Finder - 3.5/3.6 -- Stop people mass deleting / editing their posts plugin - 3.6 -- v3arcade reduce scores to keep arcade competitive -- Make guests give a name when posting or replying - 3.0

Sorry, but what you mean is that although i set someone as moderator in primary group, they don't have power to moderate the forum?

That's right.

thanks for the quick reply!

just one more question, can I enable html code for a particular usergroup(eg moderator?)

You can't do it via vB natively but there is a hack (which I've never tried): http://www.vbulletin.org/forum/showthread.php?t=96926

I can't even manually assign to each users to allow them to use html code in vB?

Per user.. No.
Per usergroup with the above hack.. Yes.

Or you can do per forum regardless of usergroup using the forum manager.

You could just assign the user as a moderator to one forum and leave his/her group as it is. Then simply edit the user, change his custom title and other looks to how to moderator class looks.