I'm not sure why you'd have to worry about interlacing with the dvx 100 24p footage. That should be progressive already isn't it?
For stuff to look good on the web I export using h264 at 15 fps with a bit rate of 500 kbs 320x240. For the audio use AAC and set it to mono. This will give you a small file and a nice looking image.
Check out this post at freevlog:
http://www.freevlog.org/index.php/2007/03/19/41-compress-for-the-web-imovie...
I know it says iMovie, but I use these settings in FCP.