Add more devices to the sample inventory.

Be more accurate in explaining PC primary, extended, and logical partitions.
I'm learning more about this stuff than I ever wanted to.

Add a "collect your network configuration" section to the pre-installation
tasks.

Add a link to the errata information.

Note that the 'c' partition refers to the enclosing slice, not the whole
disk, as I have always thought for the past seven years. Also note that
the 'd' partition is no longer special, but that lots of software,
including sysinstall, believes that it still is. Update the ASCII art
disk layout diagram to reflect this, comment out the EPS version until I
can fix it.

Fix some typos.

Some of this is my own work, the rest is based on comments from
William Roth <RothW@SEC.GOV>, and Annelise Anderson
<andrsn@andrsn.stanford.edu>