An excellent article detailing how to add PHP syntax checking, context sensitive PHP help commands, and google searching to Editplus for PHP development.
The most useful in my view is the Syntax Checker, which can be added as a user tool in Tools -> Configure User Tools-> Add Tool >> Program, and enter:
Menu text : PHP syntax checker
Command : c:\php\php.exe -l
Argument : $(FileName)
You can then map it to a keyboard shortcut using the Keyboard subtree option on the left. I have found SHIFT-S and very handy companion to CTRL-S for saving and verifying your PHP file.