This one is really easy for me to write out because I found a great how to guide at pfSense.org.
Here you go: PfSense 2 on VMware ESXi 5
The how to will walk you through the install and setup of a virtual firewall using pfSense and VMWare ESXi5. This will allow for layer 3 routing and firewall capabilities in a vSphere host. Typically a vSphere host is limited to Layer 2 networking.
pfSense is a free, open source software firewall based on a customized FreeBSD distribution. It has many features that you can check out on their respective websites. pfSense installs with minimal resource needs onto a disk or flash media, in the VM example to follow it takes less than 8GB of space and 512Mb of RAM.
I walked through the steps setting up the VMWare host in a previous post, and how to configure a virtual machine in another post. I will assume you already have a host running and a basic understanding of network addressing. If you can configure your home router you should be capable of getting this up and running in no time at all.