awk question

[Bart Silverstrim]

I'm totally drawing a blank on where to start out on this.

If I have a list of URLs like
http://www.happymountain.com/archive/digest.gif

How could I use Awk or Sed to strip everything after the .com?  Or is 
there a "better" way to do it?  I'd like to just pipe the information 
from the logs to this mini-script and end up with a list of URLs 
consisting of just the domain (http://www.happymountain.com).

Any suggestions?