I'd recommend starting with the Eclipse IDE, which is kind of a universal development/programming editor, and then getting the php-plugin. Here are some links to get you started:
Eclipse has become a pretty popular development environment for Linux, so there is lots of support out there for the application. Let me know what you think.
Actually yeah, it's pretty resource intensive. I mean, if you're on a relatively quick machine I don't think it'll be a problem, but it's definitely not "light".
I have tested a few editors a while ago. I was interested in cross-platform open source ones primarily. At the end I have chosen to continue with Macromedia Dreamwawer 8 (i actually work almost exclusively on windows) even if it's not open source nor cross-platform. It's just the one i like best and i find it easy to use.
From the ones that work on linux and that I tested the best was PHPEclipse (Eclipse + PHP plugin). As aim said it is resource intensive. The light one that i found decent was JEdit + necessary plugins.
I know people who use vim and emacs and they are very content with them, but i found it complicated to learn them and a bit over the hand.
What I recommend to you finally is that you go at PHP Editor Review - PHP IDE and see the reviews and download and test them by yourself. Most likely there's no such editor to suit all programmers, so you should find the one that suits you.