Installation of OSSEC involves some compiling, so you need gcc and make installed.
You can install both by installing a single package called build-essential.
You also need to install a package called inotify-tools, which is required for real-time alerting to work.
sudo aptitude update sudo aptitude install build-essential inotify-tools
If database support is needed mysql-dev or postgresql-dev should be installed.
Run the following command to install these packages.
# apt-get install mysql-dev postgresql-dev