Thanks to everyone that replied.  I ended up "googling" a quickie 
answer.  Ultimately this is what I have so far:

RewriteEngine On
RewriteRule ^/id/(.*) /html/our_single_listing.php?ListingNum=$1

That allows me to do a http://www.mysite.com/id/2301 like I wanted.

Bradley Miller, Owner/Programmer/Designer
AccessZone Design - www.accesszonedesign.com
Blue Springs, Missouri
Phone: 816-228-3814             Fax: 775-254-6162
Toll-free: 888-872-4420 ICQ: 48555780