In the user manual, installing the guest additions is well documented. However, where do you get the guest additions ISO?
On Linux it lives in /usr/share/virtualbox (provided you have installed it to the standard locations)
PS: Guest additions provide a lot of value addition to your guests. So, if you are looking to do anything serious, go ahead and install them. I have installed the guest additions for Windows XP and Solaris. Works like charm.
