What utility or tool that runs which under Mac OS X 10.6 can I use to extract data (icon images and strings, etc.) from old Mac OS 7 (and earlier) resource files/resource forks? (...files created using ResEdit.)
Rezycle might work for you. Let us know.
On OSX you can access the raw resource fork of a file like this:
cp resource_file/..namedfork/rsrc resource_fork
There's also the system utilities DeRez/Rez (available in OSX 10.7 and as mention by @marc as part of Xcode tools on newer MacOS versions) which allows for extraction of resource fork data into a form for use by the
Rez resource compiler - e.g. extract icon data from an Icon file:
DeRez -only icns Icon^M > icon
It should be noted that the resulting files from both of the above commands require additional processing to convert the resources to a suitable form.
See related question on Icon files.
Abet slightly unstable, the resource editor Rezilla runs under 10.7.4.