Building Mono for Debian Lenny

wget http://ftp.debian.org/debian/pool/main/m/mono/mono_2.4+dfsg.orig.tar.gz
wget http://ftp.debian.org/debian/pool/main/m/mono/mono_2.4+dfsg-6.dsc
wget http://ftp.debian.org/debian/pool/main/m/mono/mono_2.4+dfsg-6.diff.gz
sudo apt-get build-dep mono
sudo apt-get install debhelper libglib2.0-dev bison libtool dpatch libxml-dom-perl libxslt1-dev dc lsb-release libx11-dev libxt-dev zlib1g-dev autoconf automake dpkg-dev fakeroot
dpkg-source -x mono_2.4+dfsg-6.dsc 
cp changelog mono-2.4+dfsg/debian/changelog
cd mono-2.4+dfsg/
screen dpkg-buildpackage -uc -us -rfakeroot

changelog file is the debian/changelog file with this entry on top:

mono (2.4+dfsg-6~bpo50+1) lenny-backports; urgency=low

  * Rebuild on debian/lenny.

 -- Craig Box <craig@dubculture.co.nz>  Mon, 20 Jul 2009 16:26:24 -0400

If you have a GPG key set up you can build without -uc and -us, which are options saying "don't sign changes" and "don't sign source package" respectively.