I don't have time for details, but here are the bones of it:
- D/L ISO image of your Linux to Win desktop
- D/L Virtualbox; install it on Win.
- Start Virtualbox; go through the process of creating a VM (menu: Machine -> New etc)
- You should have a new (empty) VM now.
- For your new VM, go to Settings -> Storage. Under IDE controller, you should see something like a CD icon and the word "Empty". Click the icon or the word "Empty".
- This will now grant you the ability to add a file to your virtual CD/DVD device. Use the folder icon to select the LINUX ISO image that is on your Windows desktop. This will mount the image.
- Close the Settings dialogue
- Make sure your VM is selected (on the VirtualBox main screen). Click "Start". The Linux ISO file should mount and your Linux should start installing into your VM's virtual HDD.