There are some HOWTOs out there in the net which describe some automatic network based install via PXE-booting a machine from a server which has a specific FreeBSD release in the PXE-booting area and a non-interactive config for sysinstall to install this FreeBSD version on the machine which PXE-boots this.
The setup of this is completely manual and only allows to netboot one FreeBSD version. The server-side setup for the clients is also completely manual (and only allows to install one client at a time, it seems). This is not very user-friendly, and far away from the power of Jumpstart/JET for Solaris where you create a template (maybe from another template with automatic value (IP, name, MAC) replacement) and can specify different OS releases for different clients and then just run a command to generate a good config for this.
I thought a little bit how it could be done and decided to write down all the stuff (so far 160 lines, 830 words) to not forget some details. All in all I think this could be done (at least a sensible subset) in a week or two (fulltime) if you have the hardware, motivation, and time. As always, the problems are within the details, so I may be off with my estimation a little bit (also depends upon the knowledge-level (shell, tftp, dhcpd, install-software) of the person doing this).
Unfortunately I do not know if I have the hardware at home to do something like this. I have some unused harddisks which could be used in a machine which is used temporary as a test-install-client (normally I use this machines as my Desktop… if I do not use my little Netbook instead, as I do not do much at home currently), but I’ve never checked if this machine is PXE-booting-capable (VIA KT133 chipset with a 3Com 3c905C-TX Fast Etherlink XL). I also do not have the time to do this (with the current rate of free time I would expect to need about a year), except maybe someone would call my boss and negotiate something.
I can not remember any request to have something like this on the freebsd-current, freebsd-arch or freebsd-hackers list since I read them (and that is since about at least 3.0‑RELEASE). Is this because nearly nobody is interested in something like this, or are the current possibilities enough for your needs? Do you work at a place where this would be welcome (= directly used when it would be done)? If you use a simple solution to make a net-install, what is your experience with this (pros/cons)?