For over a week I have bombarded an ISP (ivillage) with a take down 
notice to which he failed to respond. How do I go about forcing him to 
take down the infringing material?

Details: it's really a clear-cut case. A blogger called Lara has 
copied one of my copyrighted photographs from my website and used it 
in her blog. I contacted her first with a request to take down the 
infringing material, to which she didn't respond.
Afterwards I sent a take down notice to ivillage.com and even included 
a part of the photograph in its original size to prove my ownership. 
This had the effect that the (known) links to the infringing material 
were removed. However, the infringing material itself remains on their 
server, and I haven't got any type of response to my take down notices 
in a week.

Location of the original:
http://franklludwig.com/catalogue/Broken%20Heart.jpg (watermarked in 
the meantime, as you can see)

Location of unauthorised copies:
http://chickchat.ivillage.com/love/The_broken_heart.jpg
http://chickchat.ivillage.com/love/The_broken_heart-thumb.jpg