VMware offers with the VMware player a program for free, which is capable of running preinstalled virtual machines on Linux and Windows. The player runs not only VMware machines, but also Microsoft Virtual Machines and Symantec LiveState Recovery Disks. With this licence free software it is not possible to create virtual machines. For that purpose you still need the VMware Workstation, GSX Server or ESX Server.
VMware is offering preinstalled virtual machines based on Red Hat and SUSE Linux in its Virtual Machine Center as free downloads. VMware is also offering a Virtual machine based on Ubuntu in its Browser Appliance Virtual Machine Center. It's no full Ubuntu, but a basic version dedicated to run as a secure browsing environment (download size: 200mb). See screenshot.
Hopefully there will be a virtual machine based on the full Ubuntu 5.10 offered soon. Please report if you find one for download.