Investigating the issue, I found that the virtual machine configuration that VMware server supplied for Ubuntu had no reference to sound devices. This was quickly fixed by adding the following two lines into the .vmx file holding the machine definition.
sound.present = "TRUE"These lines were added just after the definition for the Ethernet device. On rebooting the virtual machine the sound was enabled.
sound.virtualDev = "es1371"
My guess is that VMware defaults are designed for serious server use rather than playing with desktops, hence the lack of a default sound card in the configuration.