I have the (mis)fortune of having a large project source-base in which I am working primarily on PHP and JavaScript. I have to have the full project area as the project root
I have Eclipse for PHP Developers and I was dealing with the same issue.
In addition tot he excellent answers above, I have one more suggestion.
My first recommendation is not to use Aptana unless you actually want those validators (as they are nearly impossible to turn off from my experience).
Beyond that, go to File -> Properties -> Builders, and deselect "Validation" and "Script Builder" and "JavaScript Validator".
So far it's helped speed up some operations tremendously.
I also recommend disabling "Automatic Build". Because you're using PHP, the odds that you actually need it to build anything if you don't want validation is slim.
In the main menu, go to Project and uncheck "Build Automatically". You will want to build your project every now and then by right clicking on the project and selecting "Build Project".
All the above steps have helped me get the basic editor, which is exactly what I wanted.