Check out the whitepapers, someone posted a php walk through.
http://www.w3schools.com/ is one of my favorite sites.
http://del.icio.us/tag/php
Do a google search on tutorials and there are plenty out there.
The best way to learn is by look at examples if you already have experiance in scripting. Pick a script from hotscripts.com or freshmeat etc. something simple like a guestbook script and look through it modify it. That worked best for me.
Good luck.