No matter how you do it, backup the system (main IPEdge backup and messaging). Download both backups to your PC. It would not hurt to already download 1.7.3 OVA file. It is 4 GB and it can take a while depending on your Internet speed.

The last time I upgraded VMWare 5.5 to 6.0, it was pretty easy, pretty much just like you said. Download the new ESXi and boot to USB. We were pretty nervous when we upgraded our file server, but it ended up being pretty easy.

It would be good to know how to reinstall IPEdge if something goes wrong. I have done this a few times now due to failed systems. It is pretty easy. It is about 1-2 hours of downtime to get it fully up and running again.

The nice thing about VMWare 6.5 is that you can manage from a web browser instead of a client.