jakeb, you can use either individual emitters http://www.dripirrigation.com/drip_irrigation_info.php?cPath=38&products_id=626 or tubing with built-in tubing http://www.netafimusa.com/landscape/products/techlinecv
I planted 100 black walnuts 2 years ago and used the individual emitters. I used one per tree(the trees were seedlings), but now find it difficult to expand the number of emitters because of the way I layed out the polytube. I used the netafim drip tubing on the pecans(4-6 feet tall). I teed off the lateral line with blank tubing, then connected the emitter tubing & made a half circle around the tree. The emitter tubing has .9 gal/hr emitters on 18" spacing. It will be easy to add emitter tubing as the trees grow..du