Its been a long time since I've thought about MacOS resource forks. Are you using the classic MacOS (i.e. before MacOS X)?
As I recall, ResEdit was the application most often used to manipulate the resource fork of a classic Mac application. I know it can edit cursor resources, but I don't recall if it can read PNG files. You may need to convert the files to GIF.
ResEdit is a Classic MacOS application. MacOS X prior to 10.5 could run Classic apps in emulation, but in 10.5 this support has been removed. You'd need to find a system either running the classic MacOS directly, or running 10.4 with Classic installed.