Windows, OS X, Linux oh my! Run all three together using VirtualBox by Sun Microsystems - OS Installation
Time for the first boot! You have two options:
Use guest OS installation disk:
Insert your guest OS installation disk and click "Start" in the VirtualBox menu pane. The First Run Wizard should start. Select "CD/DVD-ROM Device" and click next. If the First Run Wizard doesn't start, use the instructions below to manually navigate to your installation disk.
Click "Start" in the VirtualBox menu pane. Once you see the blue intro screen, hit F12 immediately to select the boot device. When you see the black screen, move to the device menu as shown in the screenshot and select "More CD/DVD Images." This queues up the Media Manager. Click "Add" and navigate to the ISO (I happened to have the latest Linux release lying around). If the ISO is grayed out, it's probably corrupt.
Once your ISO is checked, go back to the black screen and select "Continue Booting." You should be greeted with a familiar start-up screen. This is the light at the end of the tunnel.
Follow the instructions on the install wizard as usual. At this point you should notice that your guest OS is using up all of the RAM that was allocated earlier. When asked where you want to install the guest OS, you should see the .vdi image that was created a few steps ago.
The installation will begin. The virtual machine may restart a couple of times. If you are supervising the installation when this happens DO NOT "hit any key" to boot from the CD/DVD drive. This will cause you to lose the current progress of the installation.
If all goes well, you hard work will be rewarded by the appearance of the desktop. Congratulations!