From Nick Shanks/SourceForge website:

"A resource editor for the Mac OS. The project compirses numerous binaries, supporting 68k, Classic PPC, and Carbon/Cocoa. It supports dynamically loaded CFM or MachO plug-ins to edit resources, and is easily extendable by third parties."

I'm not in any way associated with Nick. I just like the product he's been developing for all flavors OSX. There is no official word that it will/will not work in 10.5, but I've edited about 30 files without any issues so far.