Download the ubuntu 13.04 disk image
Run vmware player and create a virtual machine. Opt to install the operating system later.
Advance the wizard, selecting defaults. Select "Customize Hardware" when you have the option.
Specify 2GB of memory ( this may be overkill - if you don't have that much available you can experiment with less ).
Indicate that you want to use the ubuntu 13.04 disk image that you downloaded earlier for the CD.
Specify "Bridged" for the network adapter type ( if you don't care about accessing the server from the outside world, it can be left as the default which is NAT ).
Close the hardware configuration wizard and select "Play" to start the virtual machine.