parallel ports are mainly used to connect to the devices like printers.
http://en.wikipedia.org/wiki/Parallel_port
Serial ports are used to connect the console terminals like Hyperterminal for debugging.
http://en.wikipedia.org/wiki/Serial_port
in your case it looks like the base host doesnt have serial and parallel ports. thats the reason for showing unavailable.
Refer the following reference doc from VMware for the steps to configure serial and parallel ports on a vSphere VM.