If you are just using firewall logs, I doubt you will easily hammer it down to specifics.
To an untrained eye, there may be just too much traffic. Add to that a MONTHS worth of
traffic. What services do you open to the world? MAIL? WWW? FTP? If any, are they in a DMZ?
What patch level and version is your PIX?
Any IDS features turned on on the PIX? Have you used any of the monitoring in the http GUI?

I'm really not understanding the value of telling you they are going to hit you..??
Seems ripe for a trap and then game over. Why would he tell you?