Changing that last piece to say /bin/bash, when you know for sure bash is in fact installed, will do the trick. Remember to try this piece of advice with some care: first be sure what you write in there actually is verified as correct, since it's a highly sensitive system file that might just as well lock you out completely from the system if you put in even the smallest typo in there. Also, don't forget to logout and re-login to confirm your system changes.
Moving on to the actual operating system itself, I must say the installation actually went on much smoother than I had expected, even with the virtual hardware that FreeBSD had to accept. The only thing that went crazy was the X server which is forgiving when you account for the poor graphics driver that VESA is in a window inside another OS (in this case as you hopefully recall, Mac OS X). There were a lot of packages to post-install, but once I had run xorgconfig and grasped which resolution and depth to use for the mysterious virtualized Cirrus graphics card, everything was up and running without any terrible issues. It did work, after all, and the colors looked alright. It was however acting slow which I blame the lack of Parallels Tools for.
Easier than you can imagine to install if you go for the Standard Install option (found on sysinstall's ncurses menu). With the auto-configuration alternative things went well for me. I must recommend that you never run FreeBSD with an X server if you virtualize that OS, because it won't exactly be the best experience you've had in your life. If that's what you're after, why not install Linux instead? For command-line server usage, though, FreeBSD is one of the smoothest and quickest operating systems I've tried virtualize. Go FreeBSD 6.2!