This will show you how to install and configure Virtual Box on Ubuntu from the offical PPA
Installation
echo "deb http://download.virtualbox.org/virtualbox/debian $(lsb_release -sc) contrib" | sudo tee /etc/apt/sources.list.d/virtualbox.list
wget -q http://download.virtualbox.org/virtualbox/debian/oracle_vbox.asc -O- | sudo apt-key add -
sudo apt-get update
Now install the package
sudo apt-get install dkms virtualbox-4.2
Now add the extension pack to enable VRDP
wget http://download.virtualbox.org/virtualbox/4.1.0/Oracle_VM_VirtualBox_Extension_Pack-4.1.0-73009.vbox-extpack
sudo VBoxManage extpack install Oracle_VM_VirtualBox_Extension_Pack-4.1.0-73009.vbox-extpack
Set the Resolution
VBoxManage controlvm VM_NAME setvideomodehint XRES YRES BPP
VBoxManage setextradata global GUI/MaxGuestResolution 1920,1200