Assuming you have satisfactorily set up your server environment, you may now wish to put the Etherboot onto an EPROM or EEPROM. Naturally this assumes access to hardware to program (and possibly erase) EPROMs. An alternative is to use an EEPROM card. There is a schematic and PCB artwork for such a card at the web site where you got the Etherboot distribution. This EEPROM card plugs onto the ISA bus and can be reprogrammed with software. Some network cards, for example the 3Com 905B, have a socket for an EEPROM which can be programmed in situ with the right utilities. See any release notes accompanying Etherboot for more information.
Most network cards come with a blank (E)EPROM socket even though it is seldom used. When it is used, it is typically filled with a proprietary EPROM from the network card manufacturer. You can put an Etherboot EPROM there instead.
First you must discover how to enable the EPROM socket on your card. Typically the EPROM is not enabled from the factory and a jumper or a software configuration program is used to enable it.
Secondly, you must discover what size and speed of EPROM is needed. This can be difficult as network card manufacturers often neglect to provide this information.
The smallest EPROM that is accepted by network cards is an 8k EPROM (2764). 16kB (27128) or 32kB (27256) are the norm. Some cards will even go up to 64kB EPROMs (27512). You want to use the smallest EPROM you can so that you don't take up more of the upper memory area than needed as other extensions BIOSes may need the space. However you also want to get a good price for the EPROM. Currently the 32kB and 64kB EPROMs (27256 and 27512) seem to be the cheapest per unit. Smaller EPROMs appear to be more expensive because they are out of mainstream production.
If you cannot find out from the documentation what capacity of EPROM your card takes, for ISA NICs only, you could do it by trial and error. (PCI NICs do not enable the EPROM until the BIOS tells the NIC to.) Take a ROM with some data on it (say a character generator ROM) and plug it into the socket. Be careful not to use an extension BIOS for this test because it may be detected and activated and prevent you from booting your computer. Using the debug program under DOS, dump various regions of the memory space. Say you discover that you can see the data in a memory window from CC00:0 to CC00:3FFF (= 4000 hex = 16384 decimal locations). This indicates that a 16kB EPROM is needed. However if you see an alias in parts of the memory space, say the region from CC00:0 to CC00:1FFF is duplicated in CC00:2000 to CC00:3FFF, then you have put an 8kB EPROM into a 16kB slot and you need to try a larger EPROM.
Note that because pinouts for 28 pin EPROMs are upward compatible after a fashion, you can probably use a larger capacity EPROM in a slot intended for a smaller one. The higher address lines will probably be held high so you will need to program the image in the upper half or upper quarter of the larger EPROM, as the case may be. However you should double check the voltages on the pins armed with data sheet and a meter because CMOS EPROMs don't like floating pins.
If the ROM is larger than the size of the image, for example, a 32 kB ROM containing a 16 kB image, then you can put the image in either half of the ROM. You will sometimes see advice to put two copies of the image in the ROM. This will work but is not recommended because the ROM will be activated twice if it's a legacy ROM and may not work at all if it's a PCI/PnP ROM. It is tolerated by Etherboot because the code checks to see if it's been activated already and the second activation will do nothing. The recommended method is to fill the unused half with blank data. All ones data is recommended because it is the natural state of the EPROM and involves less work for the PROM programmer. Here is a Unix command line that will generate 16384 bytes of 0xFF and combine it with a 16 kB ROM into a 32 kB image for your PROM programmer.
(perl -e 'print "\xFF" x 16384'; cat 3c509.lzrom) > 32kbimage
The speed of the EPROM needed depends on how it is connected to the computer bus. If the EPROM is directly connected to the computer bus, as in the case of many cheap NE2000 clones, then you will probably have to get an EPROM that is at least as fast as the ROMs used for the main BIOS. This is typically 150 ns. Some network cards mediate access to the EPROM via circuitry and this may insert wait states so that slower EPROMs can be used. Incidentally the slowness of the EPROM doesn't affect Etherboot execution speed much because Etherboot copies itself to RAM before executing. I'm told Netboot does the same thing.