How can I install Alfresco on an existent web server, allready with tomcat and mysql installed. What files do I need to install/unzip/change to make alfresco run correctly?
Add the shared folder to tomcat http://wiki.alfresco.com/wiki/Install_Tomcat6 Put the alfresco.war and share.war files into Tomcat's webapp folder. Copy and configure alfresco-global.properties and put it into <tomcat home>/shared/classes Create an empty database for alfresco to use. You may also need third party tools like open office and image magic.
I suggest you start by using the installer, study the configuration and then canibalise it to switch to your database and AS.