Here you can follow the guide how to attach/configure VDI image with VirtualBox. You can check FAQs for Credentials( Username & Password) for VDI images. At the moment we have plans to offer you 30+ Linux/Unix distributions, we may add more to our list in near future, you can also send us suggestions if we are missing any popular distribution from our list.
We offer images for both architectures 32bit and 64bit, you can download for free for both architectures. From here you can download and attach the VDI image to your VirtualBox and use it. We offer open-source (Linux/Unix) virtual machines (VDIs) for VirtualBox, we install and make them ready-to-use VirtualBox images for you.