apt-get install mysql-client mysql-common mysql-server
change root's password
mysqladmin password db-root-passwd
edit the files in /etc/mysql/ most important is so change the max_allowed_packet to 16M
apt-get install make wget
mkdir -p /usr/local/src/rt
addgroup rt
adduser www-data rt
cd /usr/local/src/rt
wget http://www.fsck.com/pub/rt/devel/rt-2-0-12-pre6.tar.gz
tar xzf rt-2-0-12-pre6.tar.gz
This is the fun part.
basicly, keep running make testdeps until it finds everything. You'll likely need the following packages. (all in the debian archives)
make installthis will prompt you for several passwords. most of the time it wants the mysql admin/root passwords, but sometimes it wants the rt users's password. pay attention to what it says.