How about this for a quick tarp ?
http://www.instructables.com/id/Instant-Hammock/
The hammock hanger , maker is Tim Anderson, MIT guy of many daring and off the wall adventures. If you've never found your way to his web site before you've missed a treat. Don't recall the web site , just google Tim Anderson and out rigger canoes and it ought to get you there.
On a more serious note. Hammock Forums is the place to be
http://www.hammockforums.net/forum/index.php
Also find your way to Ed Speers website , of Speer Hammocks. You can find it on the fourm. Order yourself a copy of Ed's book "Hammock Camping" , $20 or so. It has complete instructions inside on how to build his version of a hammock. You can also order a hammock kit from him , or just the raw materials. Or just follow his advice about materials to use and go find 'em yourself. Or ask around on the forum.
There are also a few how-to make a hammock video on youtube, short and sweet productions. Mostly showing proper way to gather the ends and proper knots so you don't fall and hurt yourself
Heck. you could just follow Tim's method and make one out of one of your poly tarps.
D