If you set out to build your own Virtualbox Application you'll have to comply with instructions such as the following generated under Bionicpup64's Quickpet when Virtualbox was chosen on the Useful Tab:
- virtualbox-Instructions.png (21.72 KiB) Viewed 974 times
For me, attempting to compile anything is hit-or-miss, usually the latter. 
The instructions are necessary because Virtualbox is 'kernel-specific': has to be build against the kernel under which it is to be used. While Virtualbox is kernel specific, Puppys are not. 
. With rare exceptions, the file-and-window managers and other applications contained in Puppy_VERSION_Number.sfs will be fully functional under any Kernel, subject to the 32-64bit dichotomy exception.
perdido has gratiously provided virtualbox.sfses for "Many Puppies", viewtopic.php?p=1552#p1552. If your Puppy is not among those, as an alternative to building your own Virtualbox application, it may be less problematic to use one of perdido's builds and swap your Puppy's current kernel. Perdido's posts identify the kernels used. You may be able to locate an appropriate 'hugh-kernel' package. But it might be faster to just download the Puppy perdido identified, unpack its ISO and use the kernel it contains.
Remember that "a" kernel consists of the vmlinuz, the zdrv.sfs (drivers-specific to that vmlinuz) and often an fdrv.sfs (firmware which can be used with any vmlinuz). Also remember that the initrd(.?z) of your Puppy will only use appropriately named an zdrv.sfs and fdrv.sfs. For example, to be used with puppy_bionicpup64_8.0.sfs an fdrv.sfs must be named fdrv_bionicpup64_8.0.sfs