Hello,
Ardvark are you refering to a legal copy of VirtualBox? if so I have no idea sorry... Im using a copy of Microsoft Virtual PC 2007 SP1 and all is running fine maybe a bit slower with only 1gb of ram being used by it but its not slow enough to complain about.
*EDIT: I take the slow bit back with only 1gb of Ram dedicated to Windows 7 and multiple programs running outside of the virtual PC it is extra slow on THIS PC dont take my word for it though it would most likely run faster on newer machines