I browse a lot of forums myself ... I've yet to come across one that does what you are asking. Doesn't mean they aren't out there just means it's not necessarily the norm as you suggest. I know that Vbulletin, XMB, Invision and phpbb, just to name a few, are not programmed like that out of the box.
I prefer it as it is, it makes more sense (to me) to work from a parent window and use tabs (IE7 now has tabbed browsing- upgrade

). I always hated sites that had navigation that opened each new page in a new window ... by the time you were through checking out the site you have a dozen new windows to shut down. Sloppy.
So, with all due respect to your browsing habits, we will keep it as is for the time being.

I do strongly suggest, if you do upgrade to IE7, you reinvent your browsing habits and use the tabs. I did so some time back and am glad I did.
Daf