You could do worse than Wikipedia for an EMP primer:

http://en.wikipedia.org/wiki/Electromagnetic_pulse

Global Security.org: http://www.globalsecurity.org/wmd/library/report/1988/CM2.htm

US Army Corps of Engineers: http://www.usace.army.mil/publications/eng-pamphlets/ep1110-3-2/toc.htm

Disturbing article in 2001 Popular Mechanics: http://www.popularmechanics.com/technology/military_law/1281421.html

NEW: PAUL WEYRICH AT FRONTPAGE: http://www.frontpagemag.com/Articles/Read.aspx?GUID=48973533-18B4-4903-BF1A-F083C43B1667