I'm not sure what I did wrong. I created a new server (for the walrusonline.net domain). I tried to browse to it, but realized Apache wasn't running.
So, I started Apache and found that httpd.conf had syntax errors. The errors were for the following lines:
NameVirtualHost :80
...
Not knowing what it should be, I changed them to "*:80" and Apache now starts.
Maybe this is a configuration error on my part, but I basically created the domain with all the defaults and haven't really done much else. I was bouncing around Webmin after creating the domain and doing the Apache start, but I don't think I did anything that would have edited the httpd.conf file to have a syntax error, but it is possible.
Of course, a novice user like me probably should be prevented from making a bad httpd.conf file through the Webmin/VirtualMinPro interface.