How did Gamernode.com do this?
 

<a href="http://forums.gamernode.com/index.php" target="_blank">http://forums.gamernode.com/index.php</a>

If you take a peek at Gamernodes main index down towards the bottom you will see forums for Black Mesa, and HLgamer. When you click on these links you are taken to completely different looking forums with individual forums etc that still somehow seem to be using the Gamernode main vB forum database, yet all posts/threads are seperate.

Any ideas how this was done?

Those are sub-forums with a different style set as default.
To set different styles for individual forums:
AdminCP -> Forums & Moderators -> Forum Manager -> Click forum you want to edit -> Style Options -> Custom Style for this Forum dropdown menu.

I'm really not sure. Is it possible to make a subforum appear to be an entirely new set of forums like that?

Like he said, YES.

Example, my site!

http://www.houseofhelp.com/forums/

go in there, check out the corsair area at the bottom. completely different default skin. At the top of gamernode and my site, it's clear that you're still on the afforementioned forum when you're in the visually different sub-forum.

lol I'm curious how he made it seem as though a forum index was nested inside of a forum.

Note how if you click the Black Mesa Source forum button on most forums it would take you to that board. A single board. Instead it takes you to a whole new set of forums. One with subforums.

How does he get a whole set of forums within forums? Is this just done with many many subforums?

I know how to do the different styles.

Yes. Note that it is not a forum index. It is forumdisplay.

wow thats web is very beauty...
i want to make web like that..
anyone help?

I know its a work of art. The vB integration is incredibly well done.

@john1744 i need make webportal not forum. :p