Moving forum to sub directory

[mitelforums]

I've taken over a forum. 
I'll be moving it to my own server.
The original admin installed everything on the root.
I'd like to move it to <domain>/forum so I can add other things to the home page.
I've moved everything over to my test server ok but my question is this:
I'd like to try and preserve the search engine rankings as best I can.
This means I have to redirect anything that would have been originally for the forum via either a .httaccess 302 or an html redirect to <domain>/forum/index.php
Still, I'd like to keep <domain>/index.php avail for something else.    Is this possible?  -if yes, is there a howto?

Mitelforums

[Kindred]

you would use .htaccess with a [R=301,L] at the end...

however...  this would redirect everything   you could not use index.php in your root...

look up htaccess regexp....