Before you can create the new VM, you need to have the Chromium ISO setup to be used as a CD-ROM.
Use the "Virtual Media Manager..." from the File menu to do this.

Click on the Add icon.

Choose "chromium.iso" in the "data" folder at the location you extracted the, or where you downloaded the ISO to.
Click on "Open".

Now you need to make a New VM, so click on the New icon.

Click on Next.

For the Name, use "Chromium Browser VM".
For the OS, use "Linux".
For the Version, use "Ubunut".
Click on Next.

The VM requires at least 256MB of RAM, but 512 or more is recommended.
Set the amount of memory you want to use, then click Next.

Uncheck the box that says "Boot Hard Disk (Primary Master)", since we are using an ISO for a CD-ROM boot.
Click on Next.

Ignore the warning, click on Continue.

Click on Finish.

Before we can use our VM, we need to double check a few of the Settings.
Click on the Settings icon.

Click on "System" (left side of the window), and make sure the Floppy box is not checked.
Make sure the "CD/DVD-ROM" box is checked.
Make sure the "Enable ACPI" and "Enable IO APIC" are both checked.

Click on "Display" (left side of the window).
Turn the Video Memory as high as you can. Max it out.

Click on "CD/DVD-ROM" (left side of the window).
Check the "Mount CD/DVD Drive" box.
Select "ISO Image File" and choose "chromium.iso" from the dropdown menu.

Click on "Audio" (left side of the window).
Make sure the "Enable Audio" box is checked and the correct audio controller is selected.

Click on "Network" (left side of the window).
Make sure "Adapter 1" is enabled.
Set the Adapter Type to "Intel PRO/1000 MT Desktop (82540EM)".
Set "Attached to:" to "NAT".

Click on "USB" (left side of the window).
Uncheck (disable) the "Enable USB Controller". We don't use it.
Then click on "OK".

Make sure you have started Xming (for Windows users) or allowed access to your X session through "xhost".
Now go ahead and start your Chromium Browser VM.