conditional .htaccess redirect / advanced linking?

[Jeff]

I have a domain which was once an IRO which is now an IRM and I want to figure out a better way to link it with my main domain.

Here's what I have
beaverisland.net (main domain)
-- /chamber
-- /beaverislandorg (beaverisland.org IRO points here - same content as /chamber )
-- /beaverislandorg/.htaccess (current redirect here to check for old /chamber, because it was once an IRO)

When a visitor enters beaverisland.net/chamber I would prefer if the URL stayed under beaverisland.net/chamber

Now the problem is that for a while beaverisland.org was an IRO, so there are some links (including a couple printed) pointed to beaverisland.org/chamber/

So I need a way if the visitor enters beaverisland.org/chamber/anything to redirect them to beaverisland.org/anything but if they enter beaverisland.net/chamber/anything to just produce the page/directory This is the way it works above with two copies, but I would like a way to sym link or otherwise link the files under /chamber and /beaverislandorg so I would not have to maintain two copies of all the files.

One way is to create an .htaccess line like
redirect /chamber http://beaverisland.org
but this does not maintain beaverisland.net/chamber under beaverisland.net as I would like to do

Is there a way to do a conditional redirect in the .htaccess based on the domain (without too much overhead)?

Or is there a way to do a (sym) link without the risk of creating a loop from some search engine spyder? (linking /chamber/chamber back to /chamber)

It's not a big deal at all, but I'm curious if there is a better way to do it.