You can download the latest version of VMware Fusion, currently 5.0.2, directly from VMware and start by installing that. You do not need to install previous versions first and can always start with the latest release you have a serial number for.
As far as the Virtual Machine(s) go, generally speaking, you can run then from wherever you have read and write access however if you want them in the default location then just copy them back to the ~/Documents/Virtual Machines folder and double-click to load in VMware Fusion of use File > Open in VMware Fusion. You can even drag and drop the Virtual Machine Package onto the Virtual Machine Library window.