You probably need to set some dhcpd.conf options, see:
http://wiki.ltsp.org/twiki/bin/view/...sing_Etherboot
In short, for Etherboot add to dhcpd.conf:
option option-128 code 128 = string;
option option-129 code 129 = text;
option option-128 e4:45:74:68:00:00;
option option-129 "MOPTS=nolock,ro,wsize=2048,rsize=2048";
For dapper, if you installed ltsp via apt, notice that the dhcpd.conf file is actually in /etc/ltsp not /etc/dhcp3!
Kind Regards