AHA!

For anyone else who's interested you can grab the sources here:
<http://debian.httrack.com/dists/unstable/main/source/>

In case you're not running debian here's the step by step, but I should add
the disclaimer, especially since there isn't a clear link to this from the
downloads page USE AT YOUR OWN RISK. This is unstable/beta and I'm not sure if
Xavier is even looking for feedback on it at this stage.

Download the orig and any patch files then:

tar xzf httrack_3.41.15.orig.tar.gz
tar xzvf httrack_3.41.15-1.diff.gz
mv httrack_3.41.15-1.diff httrack-3.41.15/
cd httrack-3.41.15
patch -p1 < httrack_3.41.15-1.diff
Read the docs
./configure && make && make install

I haven't tested it yet but it seems to be compiling fine right now.