It is the same principle that limits the line lengths in laser drilled tubing such as this..
http://www.dripirrigation.com/drip_i...roducts_id=274
I believe the layout and the principle for Tuk50's irrigation plan is great. he has a header a water source and his layout complete. I would just replace the final runs of pvc into the irrigation zone with 1/2" poly tubing or drip tape or drip tubing. If poly line is installed emitters can be places in exact locations where water is needed. Flag drippers are probably best for the low pressure application because most PC drippers require ~4 psi to open. THe flag drippers are recomended for low pressure systems.
http://www.dripworksusa.com/store/drippers.php#tiptop