Here's a neat chart I found on the Army training material welding site http://www.adtdl.army.mil/cgi-bin/atdl.dll/tc/9-237/toc.htm
about welding polarity... Lots of other good welding info also...

<img src="http://personal.atl.bellsouth.net/rdu/e/_/e_dan/weld_polarity.jpg" alt="" />

Also have a link to this site on the "Welding" page link in the signature below..