1. Download ISO：
FreeBSD: ftp://ftp.freebsd.org/pub/FreeBSD/ISO-IMAGES-i386/8.0/8.0-RELEASE-i386-dvd1.iso.gz
2. mount ISO to local, e.g. /mnt/bsd, you can found the *-RELEASE (here is 8.0-RELEASE) folder
sudo mount -t iso9660 -o loop 8.0-RELEASE-i386-dvd1.iso /mnt/bsd/
3. cp all files under /mnt/bsd/8.0-RELEASE/src/ to your workspace, say /home/jack/bsd/pkg
cp /mnt/bsd/8.0-RELEASE/src/ ~/bsd/pkg
4. change mode of install.sh to be writable
chmod +wx install.sh
5. modify the line in install.sh
cat s${i}.?? | tar --unlink -xpzf - -C ${DISTDIR}/usr/src
to be
cat s${i}.?? | tar --unlink -xpzf - -C ../src
6. run ./install.sh all
note: all - extracting all source code, of course, you can select some
For NetBSD, mount ISO locally and browse the folders, you will find some *.tgz file, just copy and tar