In Dreamweaver, if you use include() etc, it recognises them as resources and you can then flick between them as Dreamweaver creates 'tabs' for them at the top of the page (and other resources linked from that file, e.g. javascripts etc). How can you at least make Aptana acknowledge an outside resource?
Currently I'm using Netbeans, but before this I also used Aptana 2.
In Aptana 2 it worked for me by doing this:
Maybe you have to restart Aptana. If this does not work, try to set php as primary nature. (one of this settings worked for me)