well you only have testing repositories in there, and wvdial is not in testing, therefore it fails to find it.
In fact you have no repositories other than the cdroms and security. I will leave it to someone else to suggest how you should/could add a stable or unstable repository there and obtain wvdial from there. These have some references though: http://jaqque.sbih.org/kplug/apt-pinning.html http://www.linuxmafia.com/debian/tips
