Let me start by saying I am no expert on the War Powers Act so if you stop reading at this point it is understandable.
As I understand it the WPA allows the president to engage in military hostilities against a sovereign nation provided he reports to congress within 60 days so they can decide whether or not to declare war. (Only congress can declare war, not the president.) Recall George Bush obtained congressional authorization for military action in Afghanistan and Iraq.
The 60 day WPA window is closing on the US Libyan hostilities. Barrack Obama is claiming the WPA does not apply because troops are not in harms way on the ground. By that logic, Japan did not engage in military hostilities when they attacked Pearl Harbor.