Our league has a similar scoring scheme, although more complicated (if you can believe it).
You have to do your homework, but basically the over-generalized value listing is LB, S, CB, then DL. However, there are many, many exceptions, especially at the top of the charts (i.e., Strahan gets tackles and sacks).
A lot of sites rank IDPs -- including the Cafe -- http://www.fantasyfootballcafe.com/2004 ... ensive.php
You can find a lot of valuable IDPs on the free agent list if you patiently but thoroughly watch every week. Don't make rash decisions (i.e., I am not quite yet sold on Bracy Walker), but keep an eye out for players who distinguish themselves in the first several weeks. That way, you should improve each week and make a run.