there needs to be a server setup to share
what will be the systems root. For ltsp
useage, this needs to be

/tftproot/lts/ltsroot *.example.com(ro,no_root_squash)

If you plan on using the ability of lts1.9 to
mount nfs shares for "local" access, you will
need to share a /bin, /sbin, /usr, /home.
You can theoretically just share the ones off the
pxe server, but I usally prefer to setup a 
tree specifically for exporting.