Is it possible to install zope zserver on your virtual server and run it on
port 80 instead of apache?

Yes, you have pretty much complete freedom and control to install whatever you want.

Its been a while since I played with Zope but I seem to remember that a popular configuration was to still use Apache and somehow get Apache to pass the requests on to Zope rather than use Zope's web server directly. That way you can still do other things with Apache like run a PHP script if you have to or have another virtual host that doesn't use Zope.

Cheers
Ross

I run Zope 2.7 on my Linode. It works just fine. Its default HTTP port is 8080, but changing it to 80 is one line in the config file.

Just make sure that you stop apache first.