VirtualBox for Puppy Linux
There are multiple versions of VirtualBox available here, primarily to account for many different possible Puppy and VirtualBox combinations.
VirtualBox 4.2.12 (LATEST)
VirtualBox 3.2.14 (the 3-series works better for audio with Lucid Puppies 510 through 528 as hosts)
VirtualBox 3.1.4 for Puppy 43x (with guest additions for Puppy 431, kernel 126.96.36.199)
Puppy Linux Forum Thread: VirtualBox for Many Puppies
Older Thread: http://www.murga-linux.com/puppy/viewtopic.php?t=47128