question on SPF for spam control

[David Banning]

I have just been looking over the SPF Website to list my site as a non-spam
site. My understanding is that increasingly mail servers will be listed
as spam if they are -not- listed with some credible source.

So I thought I would list my site with;

http://www.openspf.org

I have two questions. 

1. Is this a good idea? 

2. The site says that I must update my "zone file" with the following string;

3s1.com. IN TXT "v=spf1 a mx ptr mx:banning.ca mx:mail.banning.ca mx:skytracker.ca mx:mail.skytracker.ca mx:skytrackercanada.com mx:mail.optexstaging.com mx:optexstaging.com mx:smartstage.com mx:vondette.net ?all"

but I am at odds as to which zone file this would go in. Is there a 
resource for this, or could someone just let me know what needs to be 
done with this. 

The FreeBSD site and makes reference to "zone files", not -one- zone file.
Even if I know which file, I would need some guidance to where in the file.


thanks -