Not sure how macs do it but I assume you could simply associate your php files to a less resource hungry php editor. If not You could get a PC for the price of a mac memory upgrade .
 or just drag the php file into the FB editor works on a PC.
Thanks for the reply David.
On the Mac I can do what you said, drag the php file over and edit in FB, I just lose the code coloring. There is also xdebug that works in FB I should try. With the 2Mb and only FB and Safari running I'm at 75Mb free. Looks like a memory upgrade.
So I switched to Eclipse PHP PDT2.1 Carbon (FB4 plug-in doesn't work with Cocoa) and FB 4 plug-in and this frees up alot of memory compared to FB4 standalone, and the PHP editor has features as opposed to what seemed to be just text editing (for PHP) in FB4 standalone.