Netafim USA makes Techline Dripperline 1/2" poly tubing for underground installation, plus all of the related filters, connectors, drain/vent valves and other accessories. I believe that www.netafimusa.com will give you all of the line and dripper spacing info that you need for your soil type. Haven't seen it in DIY stores, but it is available at John Deere Landscapes stores for DIYers at regular retail price (around $.30 to $.40 per foot according to the 2004-5 product catalog), and I'm sure at other irrigation supply houses. Rain Bird makes a similar product, but it looks like Netafim is the pioneer in this irrigation segment.