You can do network installations over 3 types of communications links:

        Serial port:    SLIP / PPP
        Parallel port:  PLIP (laplink cable)
        Ethernet:       A standard Ethernet controller (includes some
                        PCMCIA networking cards).

SLIP support is rather primitive and limited primarily to directly
connected links, such as a serial cable running between a laptop
computer and another PC.  The link must be hard-wired as the SLIP
installation doesn't currently offer a dialing capability (that
facility is offered by the PPP utility, which should be used in
preference to SLIP whenever possible).  When you choose the SLIP
option, you'll be given the option of later editing the slattach
command before it's run on the serial line.  It is expected that
you'll run slattach (or some equivalent command) on the other end of
the link at that time and bring up the line.  FreeBSD will then
install itself at serial speeds of up to 115.2K/baud (the recommended
speed for a hardwired cable).

If you're using a modem then PPP is almost certainly your only choice.
Make sure that you have your service provider's information handy as
you'll need to know it fairly early in the installation process.  You
will need to know your service provider's IP address, the IP address 
of your provider's DNS server, and possibly your own IP address unless
your ISP supports dynamic negotiation, most do.  If you do not choose
a PAP or CHAP login you will also need to know how to use the various
"AT commands" to dial the ISP with your particular brand of modem as
the PPP dialer provides only a very simple terminal emulator and has no
"modem capabilities database".  If you choose a PAP or CHAP login you
can simply enter `dial' (without the quotes) at the ppp prompt if your
modem uses the Hayes compatible AT command set.

If a hard-wired connection to another FreeBSD (2.0R or later) machine
is available, you might also consider installing over a "laplink"
parallel port cable.  The data rate over the parallel port is much
higher than what is typically possible over a serial line, and speeds
of over 50KB/sec are not uncommon.

Finally, for the fastest possible network installation, an Ethernet
adaptor is always a good choice!  FreeBSD supports most common PC
Ethernet cards, a table of which is provided in the FreeBSD Hardware
Guide (see the `Documentation' entry in the main menu).  If you are
using one of the supported PCMCIA Ethernet cards, also be sure that
it's plugged in BEFORE the laptop is powered on!  Sysinstall does not,
unfortunately, currently support "hot insertion" of PCMCIA cards.

You will also need to know your IP address on the network, the
"netmask" value for your address class, and the name of your machine.
Your system administrator can tell you which values to use for your
particular network setup.  If you will be referring to other hosts by
name rather than IP address, you'll also need a name server and
possibly the address of a gateway (if you're using PPP, it's your
provider's IP address) to use in talking to it.  If you do not know
the answers to all or most of these questions then you should really
probably talk to your system administrator FIRST before trying this
type of installation!  Choosing the wrong IP address on a busy network
will NOT make you popular with your systems administrator!  :-)