A very informative site which contains a lot of useful information, in an easy to understand format.
Also has a simple easy to understand explanation of the often confusing subject of interlace vs. de-interlace vs. progressive video.
DigitalFAQ is the web site for the character known as "lordsmurf" on the Restoration forum of VideoHelp.com. It looks like he has updated some pages since the last time I looked there. If you want an even more detailed description of interlacing with better pictures see www.100fps.com which his page has a URL.