What he means is that only one of your 3 servers contains the installation files, and installation is done via that machine (usually with NFS). Open a console and type "man exports" (sans quotes) for more details.
Here is the portion of my /etc/exports file that I use to enable network install:
/var/ftp/pub/ *(async,all_squash)
/var/ftp/ 192.168.0.1(rw,async) \
/var/mandriva/ *(rw,no_root_squash,async)
/var/mandriva/ 192.168.0.1(rw,no_root_squash,async) \
FTP and mandriva are separate drives that are mounted on /var. /var/mandriva contains all of the installation files from the installation disks and are located in subfolders "main", "contrib", "updates", etc.
Go to
http://www.google.com/linux and search for "Network Install".
HTH,
Michael