You can use the netboot support to download OS images from a network.
Nearly all the device drivers are coming from the network-based boot
loader, Etherboot. Please visit its web page. They have rich
documentations so you will be able to get useful information from there.
The URL is <http://www.slug.org.au/etherboot/>.

These below are common options for configure. Perhaps you may not need
to specify them.

--disable-packet-retransmission
  Turns off packet retransmission. Use it on an empty network, where
  no packet collision can happen.

--enable-pci-direct
  Define this for PCI BIOSes that do not implement BIOS32 or not
  correctly.

Here is the information about the device drivers. They are all disabled
by default, so you must specify configure options to enable drivers you
want to use. Some drivers have extra per-driver options, so the extra
options are also described below.

Caution: You should enable them as you need. Don't enable any
unnecessary driver, because GRUB might crash if you include too many
drivers at the same time.

3Com503, aka Etherlink II, also /16 model
  --enable-3c503
  --enable-3c503-shmem
    Use 3c503 shared memory mode.
  --enable-3c503-aui
    Use AUI by default on 3c503 cards.

3Com507
  --enable-3c507

3Com509, ISA/EISA
  --enable-3c509
  --enable-3c509-hack
    Send two bootp packets before waiting for a reply to the first.
    Makes a 3c509 do bootp quicker.

3Com529 == MCA 3c509
  --enable-3c529

3Com90x
  --enable-3c90x

Crystal Semiconductor CS89x0
  --enable-cs89x0
  --enable-cs-scan=LIST
    Probe for CS89x0 base address using LIST of comma separated hex
    addresses; increasing the address by one (0x300 -> 0x301) will force
    a more aggressive probing algorithm. This might be neccessary after
    a soft-reset of the NIC.

Intel Etherexpress Pro/100
  --enable-eepro100

SMC 83c170 EPIC/100
  --enable-epic100

EXOS205
  --enable-exos205

Lance PCI PCNet/32
  --enable-lancepci

Linksys LNE100TX and other NICs using this Tulip clone chip
Netgear FA310TX and other NICs using this Tulip clone chip
Tulip clones based on the Macronix 987x5
  --enable-ntulip

NE1000/2000 and clones (ISA)
  --enable-ne
  --enable-ne-scan=LIST (0x280,0x300,0x320,0x340)
    Probe for NE base address using LIST of comma separated hex
    addresses.

Novell NE2100 (Lance based, also works on NE1500)
  --enable-ne2100

NE2000 PCI clone (RTL8029)
Winbond 86C940
Compex RL2000
KTI ET32P2
NetVin 5000SC
  --enable-nepci
  --enable-compex-rl2000-fix
    If you have a Compex RL2000 PCI 32-bit (11F6:1401), and the probe
    hangs in "Probing...[NE*000/PCI]", try enabling this fix... it
    worked for me :).

Racal-Interlan NI5210
  --enable-ni5210

Racal-Interlan NI6510
  --enable-ni6510

Realtek 8139
  --enable-rtl8139

Schneider and Koch G16
  --enable-sk-g16

SMC9000
  --enable-smc9000
  --enable-smc9000-scan=LIST
    List of I/O addresses to probe.

Tiara, Fujitsu Lancard
  --enable-tiara

Old base driver for Tulip clones
  --enable-tulip

Rhine-I, e.g. D-Link DFE-530TX
Rhine-II
  --enable-via-rhine

WD8003/8013, SMC8216/8416
  --enable-wd
  --enable-wd-default-mem=MEM (0xCC000)
    Default memory location for WD/SMC cards.


The description about how to use the support can be found in the GRUB
manual. Run "info grub" in the shell prompt.