I figured out another work around. My browsers were using the cached address. So I went to another machine I've never used to access the site and edit the host file on it with entires for both
www.mydomainname.com and mydomainname.com. I confirmed it only knew of these by pinging from command line. Then I used the browser and connected to the site as though I was going to the "live" site. I was able to log in no problem. I then changed the settings you mentioned to
http://123.456.789.123. Went back out and edited my host file back out. And I'm able to access the site no problem now via IP address!
Now on to getting the ad system, mailer system, and a few other things running. Thanks for the help.