small lan parties are fairly easy to get up and running themselves.  but a large
lan party, is not just simply having more computers there.  you will more than
anything need people to help you, and also you will have a lot more things to take in to
consideration.

have your guests bring their computers with network cards installed and configured (not
just in the machine -- actually installed with the drivers). i  n addition to the
network card drivers, they should install the tcp/ip protocol which is fairly easy to do
in windows under control panel/network.  if people don't have tcp/ip installed you
had better have some windows os install cd's lying around.. because they'll be screaming
for them.

now you have 40 computers with network cards, but still no network.  i suggest hubs
(or switches) and cables.  unless you have money to burn, you are probably relying on
guests to bring hubs and cabling.  however, in order for everything to run smoothly
you should plan to have extra hubs and cables on hand since people will forget or just
won't turn up.  cable you can buy cable already crimped or you could buy a large roll
of cat 5 a large number of cable ends and crimp the cable you self.

we would advice actually having the cable not relying on people to bring their own and
simply lay down the cable under the tables and tape it to the table where the person will
be setting up their pc, and also have the ip number there too.  this way they come in
sit down and plug-in and just little entering of their ip number and they are set. also at
large lans, you will be keeping a name list of who is there, also write down the ip
address they are using just in case they lose/forget what ip they are supposed to use.
avoid having wires(cross-over cables specially) running over the floor where people will
be walking... all it takes is one clumsy jackhole to bring your whole network down becuase
he doesn't watch where he's walking.  go through the ceiling or (better yet) arrange
your tables so that you can just run the cables underneath.

we recommend that you draw up a floor plan before you start. tables laid out, and assign
places to put hubs and switchs and wiring too.  this will make it easier to get setup
faster, make sure you start this several hours before the lan is too begin... even days if
you can get access to the venue.  don't be too confining when assigning room. 
remember, roughly 3 feet for each person and enough room for people to stand behind them
too, without crowding the place over.

dedicated servers are also important for large parties.  it is best if you can get
your hands on the servers beforehand to configure them, test them, and install any
mods/games you want for your party.  while not required, we highly recommend you run
nt or linux, since windows 95 doesn't handle multiple game servers very well at all.
  the faster the machine (and the more ram it has) the more servers you can run on
it.  nothing beats running your entire lan party off two dual-p2-300 servers.
the fewer servers you have, the easier it is to manage and configure them.  we
suggest setting up batch files to run different mods and placing them on the desktop. that
way anyone can come in and start a server quickly.

you can do ip address assignment by just giving out post-its, but if you really want to
impress your guests, you can set up a dhcp server.  you can search for a shareware
dhcp server on the net, but if you have a machine with windows nt server, you have
everything you need.  configuring a dhcp server isn't a walk in the park, but it
isn't hard either.  just add a new subnet with a valid range of addresses of
192.0.2.2 to 192.0.2.254 and you should be fine (use .1 for the dhcp server itself).
   now clients just need to set "obtain an ip address automatically"
in their tcp/ip setup and as soon as they plug into the network they will be ready to
roll. post-it notes should be kept around as a backup if the dhcp server goes down or has
trouble.

at large parties, you will need help.  get several people to help you, they won't get
a lot of gaming done .  you will need people to watch the door, get names, take
money and give out info packets if you have them and finally, look after the servers.
  also have about 1-2 people to help people setup on to the network, also a few who
have problems.  if you are running leagues assign one person to each league to get
signups of people entering, record scores and keep track of who is winning and arrange the
games too.  have somebody to help just scout around and clear out junk and to answer
peoples questions.

at large lans you will have people wanting to transfere files.  assign a time for
this ... general the morning when people are slow getting start with the lan.  this
will reduce packet loss on the network.