It is not ending at all - the series of problems using Cisco OVAs within my VMWare Workstation installation. After solving some minor issues I found out that VMWare got shipped with a pretty old OVF-tool. Hitting to the VMWare site and downloading the new one took me one stop closer.
The OVA can be directly converted to a VMWare Virtual Appliance by using ovftool.exe (located in the program directory of ovftool). It is pretty straight forward
ovftool.exe <location of the ova file> <location and name of the VMX file>
After that, the ovftool starts creating and converting any OVA to a VMWare Virtual Appliance. In the meantime you can read through the ovftool documentation - it is a very amazing tool at all.