VirtualBox can read the ISO file directly. Just use the Virtual Media Manager and add the file on the "CD/DVD Images" tab. You can either mount the CD/DVD in the virtual machine settings or while the machine is running, use the Device menu for the virtual machine.

I also recommend that you make the virtual hard disk's maximum size larger than you need since the space taken up on the actual disk is based on what you use, not the size limit. I usually make my drives 16GB. The size setting is mostly to avoid letting the size of a disk grow beyond a reasonable size in case of a problem or faulty application.

Here is how to set up Linux in a virtual machine.

• Download the ISO image for the Linux insall disc
• Install VirtualBox in the Host OS
• Add the ISO image using the virtual media manager
• Create a new virtual machine
• Create a virtual hard disk
• Start the new virtual machine (which won't boot yet)
• Use the VM devices menu to mount the Linux install disc (ISO image)
• Reset the virtual machine
• The install disc will boot inside the VM
• Install Linux normally as if it was a real computer
• Boot Linux normally and log in
• Use the "Install Guest Additions" command from the devices menu
• Start a terminal session as root
• Mount the Guest Additions disc in Linux (if necessary) "mount /dev/sr0 /mnt"
• Run the "VBoxLinuxAdditions-x86.run" or "VBoxLinuxAdditions-amd64.run" file on the CD
• Reboot Linux
• Drag the VM window to the size you want or use Ctrl L for seamless mode

You may want to put the mini toolbar for seamless mode at the top of the screen, out of the way of the task bar or command bar. Do that in the general settings for the virtual machine. I've found that disabling 3D acceleration for a VM is faster unless you really are trying to use all the desktop effects and eye-candy in Linux. If you want to use 3D I recommend getting everything working without it first.

If you have any trouble installing the Guest Additions you can also boot Linux Mint in recovery mode, to a root prompt. Then install or reinstall Guest Additions.

The VirtualBox help is relatively good, though it can sometimes be hard to locate the information it covers most things that you will need to know for using it. There is a lot more information and you can ask questions in the forums on the VirtualBox site. VirtualBox 3.1.2 is quite reliable and that is the latest version.

Until you install the Guest Additions, you will have to click somewhere in the VM window to capture the mouse and keyboard for the virtual machine. After you capture the mouse it will remain inside the VM window. The keyboard input will go the the VM. Press the right hand Ctrl key to un-capture the mouse and keyboard, and press that again to re-capture them. You can also use right Ctrl with other keys to perform various commands. Click on the Machine Menu to see many of the commands. The "Host" key is right hand Ctrl by default.

After installing the Guest Additions the mouse will just move between the VM window and the normal host desktop. You can use seamless mode to combine the VM application windows with the normal desktop. Use the "show desktop" icons or commands in either OS to reveal the entire desktop. Right Ctrl L will switch quickly between normal and seamless mode, and right Ctrl F will switch into or out of full screen mode. You must be in normal (one window) mode to switch into seamless or full screen mode. You can't switch directly between seamless and full screen. The guest additions also integrates the clipboard between the operating systems and allows you to map shared folders in the host OS.