I have been having issues trying to install Zend Server on Ubuntu 10.04 following the steps here http://files.zend.com/help/Zend-Server-5-Community-Edition/zend-server.htm#deb_installation.htm
the problem was because there is a missing dependency for the “libmysqlclient15off” MySQL client library
to solve this, I had to install “libmysqlclient15off” from here (select the one that matches your architecture)
http://archive.ubuntu.com/ubuntu/pool/universe/m/mysql-dfsg-5.0/
Then install it using the command line :
dpkg -i libmysqlclient15off_5.1.30really5.0.83-0ubuntu3_i386.deb
after that running the installation for Zend server from through repositories, will work with no interruptions.