Hi,
You could use VMware vConverted Standalone and P2V the physical Exchange server to an external disk, NAS, etc. Then you'd need to wipe your physical server and install ESXi on it, configure it and then copy the VM you created with vConverter over.
For this though, make sure you:
- Make a full Exchange backup to an external disk (if you care about the data, do this!)
- Make sure that the server you use for ESXi is on the HCL, and if it is, make sure you upgrade it's firmware, BIOS etc. Enable virtualization specific CPU settings on the BIOS.
Worst case scenario, you could always power up the VM on a VMware Workstation if you need to.