The netinstall kit can be downloaded from here.
Unpack it and see the README file for instructions.
Current Status
Here is the status of netinstall of zfs boot, as of the dates
shown below:
May 31, 2007
The kit accessible through the link above works with build 65 and build 62.
It does not work with either build 63 or 64, due to bug 6553537 (zfs root fails to boot from a
snv_63+zfsboot-pfinstall netinstall image)
July 5, 2007
Apparently, the kit above has never worked for
the SunFire 4500 or the SunFire v20z, due to bug 6550500 (zfs boot
fails due to failure of ldi_open_by_devid()). However, the
fix to 6528732 (ZFS should store physical device path in addition
to /dev path) works around 6550500. The fix to 6528732 was
putback into build 68. So for platforms that do NOT exhibit
the bug described in 6550500, all builds from 65 to 68 should
work with the netinstall kit. For platforms that DO exhibit
6550500, build 68 is the first build on which netinstall of
zfs boot will work.