Good intro on the most comment types of attacks and how they work,you can also check out other securtiy related articles i have written in the security section.
http://www.teknickel.com/site/index.php?option=com_content&task=view&id=47&Itemid=56
http://www.teknickel.com/site/index.php?option=com_content&task=view&id=47&Itemid=56