BalanceNG needs the ability to operate the connected, physical interfaces in promiscuous mode. In a VM setup this requires that the VM has the permission to do that in turn.
Here is the information in the ESX Server 3 Configuration Guide for enabling promiscuous mode on the virtual switch (Pages 50 and 51): vi3_35_25_3_server_config.pdf .
For ESX version 2 you may look at this PDF from VMware and do the reverse as suggested on page 8: esx2_security.pdf.
In some cases you need to convert the VM before with the free VMware converter tool available here: www.vmware.com/products/converter/.
If VMware vSphere is being used, the Security Policy settings “Promiscuous Mode”, “MAC Address Changes” and “Forged Transmits” need all to be set to “Accept” (see Edit Security Policy for a vSphere Standard Switchfor further information).