IDE starting out any good text editor is enough, get one that has PHP
syntax highlighting to save a lot of debugging.
If you were on Linux (which your ASP reference probably means you are
a Windows guy) I would suggest Kate and also Quanta as a full IDE.
For windows I heard a few posts that notepad+ is a great tool, though
I've never seen it I do know from experience that 'notepad' that's in
Windows already is not as good as it does DOS linebreaks and a lot of
PHP code you may find uses unixy type line breaks (which makes all the
lines into one big messy one in notepad.)
For books:
For the absolute noob I would look at PHP in easy Steps (a Barnes &
Noble book) it does not go into writing secure PHP but it gets the
user confortable with PHP without scaring them.
For intermediate book, or for someone transitioning to PHP Peahpit
Press' Visual Quickstart Guide to PHP is really good, cover a lot more
ground, provides lot of examples and is very eay to either read from
cover to cover or to use as a reference.
Past that I would get O'Reilly Programming PHP, co-authored by the
creators of PHP it covers the language quite well, though it is sparse
on sample code it gives great examples of how the commands all work.
Many of the other PHP books I've seen are sample code books which are
nice but only show you a particular way of doing things, I like to
look at them to get ideas of how to do stuff, sometimes using their
code.
Lastly the ABSOLUTE BEST resource past an introductory book is PHP's
on-line documentation at php.net, it covers all the commands and
functions with great examples followed by even more useful discussions
about those commands (usually suggesting alternative approaches or
better examples than the original entry.) http://www.php.net/manual/en/
Though I usually get to it from Google searches on what I'm looking
for.
Good luck
Larry
P.S. once you get into the language but before you do anything mission
critical, read some of the PHP security articles first, such as:
http://www.sitepoint.com/article/php-security-blunders this and others
will get you a long way in being aware of what things to watch out for
when writing code.
