To follow-up on this comment, I'd like to mention that both Juan and I use Eclipse
with the PHPEclipse
plugin to do our OJS development. Both are open source (free), and are quite powerful when it comes to handling PHP projects like OJS.
Some of the nice features include strong CVS integration, so it takes care of updates/commits nicely in the GUI; as well, project-wide regex-capable searching is useful; as is code-folding and method/property auto-completion. Apparently it has an integrated debugger with breakpoints and things as well, but I've never used it (I'll openly admit to echo statements; Juan prefers writing to the error log).
It's written in Java (I believe), so it's available cross-platform - definitely on Windows XP, but the downside is that it takes a bit of a hefty computer to run it. Definitely worth a try if you're looking for a decent PHP GUI, and certainly the best I've ever seen.
OJS Development Team