"Afaik cada máquina precisa de um núcleo de cpu dedicado".
Não é assim. Seu computador multitarefa, permitindo que ele execute mais de um programa por núcleo. Por exemplo, o Virtualbox roda muito bem com uma CPU de um único núcleo, ao lado de seus outros programas.
Os requisitos para a execução do VirtualBox incluem:
Para executar o VirtualBox em sua máquina, você precisa:
Reasonably powerful x86 hardware. Any recent Intel or AMD processor should do.
Memory. Depending on what guest operating systems you want to run, you will need at least 512 MB of RAM (but probably more, and the more the better). Basically, you will need whatever your host operating system needs to run comfortably, plus the amount that the guest operating system needs. So, if you want to run Windows XP on Windows XP, you probably won't enjoy the experience much with less than 1 GB of RAM. If you want to try out Windows Vista in a guest, it will refuse to install if it is given less than 512 MB RAM, so you'll need that for the guest alone, plus the memory your operating system normally needs.
Hard disk space. While VirtualBox itself is very lean (a typical installation will only need about 30 MB of hard disk space), the virtual machines will require fairly huge files on disk to represent their own hard disk storage. So, to install Windows XP, for example, you will need a file that will easily grow to several GB in size.
A supported host operating system. Presently, we support Windows (XP and later), many Linux distributions, Mac OS X, Solaris and OpenSolaris.
A supported guest operating system. Besides the user manual (see below), up-to-date information is available at "Status: Guest OSes".