This is probably a retarded question.
>If I simply install apache2, forward ports and put some HTML in there, is it secure?
if so,
>If I install apache2 and php, forward ports and put some simple PHP script that echos back Hello World, is it secure?
When I say secure, I mean that my server won't have anything that gives the user shell access, anything that lets a user view files outiside of directories, etc.