I wanted to install a FreeBSD 7.0 system under VirtualBox, so I downloaded the ISO images (via Bittorrent). However, I couldn't find a bootable DVD ISO image, just the CDROM ISO images, which splits the distribution up into 4 different ISOs. This was awkward to handle with VirtualBox, so I decided to try to merge these into a DVD ISO. This turned out to be fairly straight forward, by simply copying all the content into a directory on my Linux box, and then create a bootable ISO image.

For details, see the script available at ftp://ftp.ogre.com/pub/leif/bsd/make_fbsd_iso.sh

Update

FreeBSD (at least v7.0) is incredibly unstable under VirtualBox. This seems to be a long time outstanding bug with Virtual Box (see VB ticket), which still seems to exist in v2.10. I've tried a few of the suggestions, but nothing seems to really help (although, I haven't tried the FBSD kernel "patch" to work around this bug). Quite annoying...