(12-15-2008 2:00PM Pacific)
I just built Haiku on OS X 10.5.6 with the latest SVN and made it into a VMWARE Image.
I then used VirtualBox and added a 2GB .VDI drive; formatted the new Virtual Disk, and mounted it then used Tracker to copy over all files from the haiku VMWare image, and issued the makebootable command on it.
After stopping and reconfiguring the VirtualBox to use the new drive, everything worked perfectly and Haiku is running with 512MB RAM, 32MB Video, and 2GB Expanding Disk (networking using Intel tied to my airport) flawlessly.
I decided to zip and upload the expanding .VDI image in case anyone else would like a ready made package to play with and not having to do all the dirty work.