dhcpd/tftp server subservient to another tftp server

[Kent West <westk@acu.edu>]

I'm trying to put together a proof-of-concept thin-client Debian 
computer lab at my university.

Here at the university, we have a centralized RIS (Remote Imaging 
Server? Microsoft?) that provides a means whereby Tech Support can 
instruct a client PC's BIOS to boot off the network (PXE) and then pull 
down a Windows image for that PC for a fresh "rebuild".

In my test lab, I've set up a Debian box with dhcpd3 and a tftp server. 
(Be aware I don't know what I'm doing.) I've configured 
/etc/dhcp3/dhcpd.conf to feed fixed IP addressed to specific client 
machines via their MAC layer addresses. Here's one section of that conf 
file:

host bi-19x {
  hardware ethernet 00:03:47:16:e2:58;
  fixed-address 150.252.x.y;	# x & y to protect the innocent
  filename "/lts/2.4.22-ltsp-1/pxelinux.0";
}

When I boot the client pc ("bi-19x"), it gets the IP address 150.252.x.y 
from my dhcpd/tftp server, as indicated by the BIOS's PXE messages. But 
then, instead of finding the pxelinux.0 file on my dhcpd/tftp server, it 
finds the campus's central RIS server instead.

How do I get my client to get my tftp offering instead of the RIS 
offering? BTW, the RIS server is on a different network segment.

Thanks!

--
Kent