Is there any way to import content from another site so it dynamically changes the content of your site? For example, I'm working on a web page for a yacht club and I wanted a section on current weather. NOAA weather has a frequently-updated site with current conditions and I want to be able to import those conditions to my site (I can do it now with an I-frame.)

Most of the time all you have to do is link the site. Here is the code from NOAA's weather map:
<img src="http://www.nws.noaa.gov/forecasts/graphical/images/Tthumbnail.jpg" alt="Click here for latest NOAA National Weather Service forecasts of high and low temperatures and more in a graphical format." width="150" height="101" border="1">

example of what it looks like - http://www.westga.edu/~stu9820/noaa.htm

I'm not sure about permissions but I'm sure is you put NOAA WEATHER FORECAST somewhere near the image it should be alright.