[pmwiki-users] htaccess redirect if not exist

[pmwiki at 911networks.com]

Hi,

I have a website where pmwiki is installed in the root. I've decided
to rewrite the website.

1. I want to move the site to /pm1/site-existing
2. I want to install a new site in /pm2/site-new

Most of the pages will be rewritten, so it will take a while, I
expect a couple of monthes, but the pagenames will be the same.

What I'd like to happen is that the default becomes /pm2/site-new and
if the webpage requested doesn't exist in /pm2/site-new, then switch
to /pm1/site-existing where the existing page is still there.

OR 

Is there a better way?

-- 
Thanks
http://www.911networks.com
When the network has to work