A problem at work the other day was every time our virtual machine cluster went down we had a bunch of virtual FreeBSD boxes that had to be manually connected one by one to our Windows share to offload reports. I wanted to make this happen automatically on boot since it was always the same Samba share.
1) Add a line to your fstab file located in /etc/fstab:
//USERNAME@SERVER/Mount_Folder /blah smbfs rw,noauto 0 0
2) Create a file called .nsmbrc located at /root/.nsmbrc and add your credentials:
[SERVER]
addr=x.x.x.x
[SERVER:USERNAME]
password=xxxx
3) Create a startup script. FreeBSD already has one available at http://www.freebsd.org/cgi/cvsweb.cgi/src/contrib/smbfs/examples/smbfs.sh.sample. This file simply parses through your fstab and mounts each SMB entry. Put it in /usr/local/etc/rc.d/ and give it executable permissions.
4) Reboot and you should be good to go!
Notes: Make sure the SERVER and USERNAME in the .nsmbrc and fstab file match exactly and are both capitalized. The username for Samba shares is not case-sensitive so just go ahead and capitalize it.