Sun virtualBox one of the best virtualization applications you can use to run multiple operating system in the same time, but it need some dependencies to get better performance in your operating system whatever the operating system is Ubuntu, Mandriva, Fedora, Centos, …… I am using it now on Ubuntu.
Ubuntu Swap, ” check your operating system Swap ”
really important because it used as same as your installed memory RAM, check this post for ubuntu Swap improvement, just make sure your swap size at least as same as your installed memory RAM.
for system setting you raise to the half memory you already have, for that if raised more than you have the Swap will help to keep you system stable.
also you can use multiple cores if you have multiple core processor. If you have a decent machine you can active full acceleration.
set the display memory depending in you graphics card performance, if you want to get 3d, 2d visualizations it might slow down the virtual machine.
that’s it for now.