Over the past few months I recall that I've been asked on several occassions how to configure multiple Apache Virtual Hosts for multiple JRun server instances or multiple JRun clusters (with or without ColdFusion).

This topic is actually explained very well on page 4 of an article written by Brandon Purcell a few years ago, and is still relevant to current versions.

Installing and Configuring ColdFusion MX 6.1 Multiple Instances with IIS and Apache Virtual Hosts