Compile 2.0 Package under 1.3?

[Stef Hoesli Wiederwald]

How can I compile the newest Smail Debian source under Debian 1.3.1?
Doing 
dpkg-source -x *.dsc
and
./debian/rules binary
resultes in:

/bin/sh: ./debian-defs.sh: No such file or directory
make[1]: *** [install] Error 1

Stef