I've tested this on a number of systems, and the result is always the same. When I install RH6.0 using the bootnet.img to do an ftp install on a machine that uses DHCP it fails to properly get the DHCP information. In particular, it WILL get the IP address, but it WILL NOT get the DNS servers, or hosyname, the have to be entered manually in /etc/resolve. This problem does not occur when doing an install using NFS or locally from a CD-ROM. I've tested this on multiple machiens using different ethernet cards.
This issue should be resolved in release 6.1 of Red Hat Linux.