Okay, so I managed to install guest additions, and now I am having mouse integration which is pretty neat.
However, I read the link which dave provided and apparently, I need to emerge the virtualbox modules in order to get USB support working. This is going to be a problem...I don't have internet access on my current Sabayon machine.
Is there any way to compile and install these modules offline from source or something like that? Any links and tips I could get would be really helpful!
Edit: If I can get a network share going which lets me transfer files from my home folder into my XP vm I don't need USB support at all...for now atleast. Can someone also please please please tell me how to setup a working network share between my VM and host system?