[CentOS] DHCPD

Not sure if there is a DHCPD/PXE forum so I will ask here.

I have been trying to get netboot to work (i.e. a machine with nothing on it
but a NIC card, no linux, no operating system, whatever) boots up and receives
a file from a dhcp server.  This dhcp server gives it all the Linux stuff
it needs so a full install can be done over the network.

I actually got this working by turning my desktop into a DHCP server and
placing the Linux images.  My problem?  Now everyone, especially with windows
machines, is complaining that their machine keeps telling them "unknown 
network" and "no internet connection".  Oops, my DHCP server was intercepting
all the other DHCP requests normally for our actual router (192.168.5.1).

I can get around this by unplugging my machine from the LAN and just having
it on a very small network with only two IPS (my desktop DHCP server and
the machine doing the boot).  However, I would rather stay connected to the
LAN especially if I have to go out over it to get an install package (like
DDD).

Can I somehow tell my desktop only to handle PXE requests and anything
else should go to 192.168.5.1?

Couple minor questions but I can save time asking here too:

I can't figure out the correct "option" or keyword to assign host name
via DHCP.

Is there a way I can have a user choose whether to install 4.5 or 5.4
(CentOS) via boot?  I put multiple choices into the C0 file but it ignored
all but one.