I got it working on a by following the steps in this post (see Post #5)
http://forums.macosxhints.com/showthread.php?t=80054
I also used this
http://www.apluskb.com/scripts/How_d...nswer2165.html
to create the .htpasswd file that the first link requires. To connect, I just put the url
http://myipaddress/ical (which is the folder the first link tells you to create, name it whatever). And then that same address into the iPhone app, and it worked perfectly.