This is an example install.cfg, referenced in my PXE article.
# Turn on extra debugging.
debug=YES
# Ok, this ought to turn off ALL prompting, don't complain to me that
# you lost a machine because you netbooted it on the same subnet as this
# box
nonInteractive=YES
noWarn=YES
tryDHCP=YES
# My host specific data
domainname=private.submonkey.net
# DHCP does this for us - if yours doesn't, specify hostname
#hostname=quinch
# Which installation device to use
_ftpPath=ftp://ftp.FreeBSD.org/pub/FreeBSD/
netDev=fxp0
tryDHCP=YES
mediaSetFTP
# Select which distributions we want.
distSetDeveloper
# Now set the parameters for the partition editor on ad10.
disk=ad10
partition=all
bootManager=standard
diskPartitionEditor
# All sizes are expressed in 512 byte blocks!
ad10s2-1=ufs 1015260 /
ad10s2-2=swap 2097152 none
ad10s2-3=ufs 8116124 /var
ad10s2-4=ufs 8116124 /usr
ad10s2-5=ufs 12180188 /usr/local
# Let's do it!
diskLabelEditor
# OK, everything is set. Do it!
installCommit