Update, April 20, 2014:
Here's a newer version of this post, with a downloadable vdi package
Unfortunately, the virtual image was unusable: even at two gigabytes of memory (the most allowed by the vm) it was painfully slow, and using the dash was basically impossible.
It's been terrific so far, and the setup was simple:
sudo apt-get install xorg fluxbox fluxconf
apt-get install dkms build-essential linux-headers-genericAnd then requested the guest additions from the VirtualBox menu: Devices -> Install Guest Additions which "loads" the guest additions virtual disk. Under gnome or kde the disk gets mounted automatically, but in Fluxbox I had to mount it myself before running the install script:
sudo mount /dev/dvd /media/cdrom cd /media/cdrom sudo sh ./VBoxLinuxAdditions.run