I have a plone zinstance set up through Apache Proxy on OS X Server 10.5. The server is set up with a single vhost on port 80, with Proxy & Proxypass directives to the Plon
Set up a static URL that will not be proxied but served from Apache directly, like this:
ProxyPass /static !
ProxyPass / http://localhost:8080/VirtualHostBase/http/server:80/Plone/VirtualHostRoot/
ProxyPassReverse / http://localhost:8080/VirtualHostBase/http/server:80/Plone/VirtualHostRoot/
Then configure /static to contain your static content.