Here are the sources for the ubuntu 64:

sudo apt-get install kdelibs4c2a
wget archive.ubuntu.com/ubuntu/pool/universe/k/kdiff3/kdiff3_0.9.92-2ubuntu1_amd64.deb
wget launchpadlibrarian.net/13473513/libkonq4_3.5.9-0ubuntu7_amd64.deb
wget launchpadlibrarian.net/10679966/kdiff3-doc_0.9.92-2ubuntu1_all.deb
sudo dpkg -i *.deb

Enjoy it!

Thank you.
Here are the steps from this solution:

sudo apt-get install kdelibs4c2a

wget http://launchpadlibrarian.net/10679965/kdiff3_0.9.92-2ubuntu1_i386.deb

wget http://launchpadlibrarian.net/13473685/libkonq4_3.5.9-0ubuntu7_i386.deb

wget http://launchpadlibrarian.net/10679966/kdiff3-doc_0.9.92-2ubuntu1_all.deb

dpkg -i *.deb

Same problem for me, and i found the following site to install kdiff3:
https://bugs.launchpad.net/ubuntu/+source/kdiff3/+bug/260326/comments/14

I tried to find some alternative comparer for kdiff3, as it no longer available on ubuntu 8.10.
And I found the alternative way to install kdiff3 without using apt-get.

sudo apt-get install kdelibs4c2a
sudo dpkg -i kdiff3_0.9.92-1ubuntu1_i386.deb

You will need to download the kdiff3 package from the kdiff3 site: kdiff3.sourceforge.net/