Virtual Box creates a .VDI folder in which each operating system is installed. It is actually much smaller in size that you originally allocated on the original installation of the OS.You can then copy this folder to an external drive, DVD, or an empty partition to backup. After the clean install of PCLOS, install VBox and set up your OS this way. Recreate the name of the OS as before. Instead of created a new hard disk, use existing hard disk. Just put the vdi file where you know where it is. I prefer to keep my vdi file in a folder in a very large data partition, instead of /home where VB creates it. Click next then it bring you to the VBox startup screen as usual with the name of your OS. Now you have everything back just as it was. I have used the same VDI folder of my Win XP in different computers, and for similar reasons as yours