The hard drive is a standard 2.5" IDE device, exactly the same as those used in 90% of all laptops out there.

However, the floppy drive is a completely different matter, its the same interface as whats used on classic desktop Macs, just with a smaller, more PowerBook-friendly cable and connectors. The only drive you can plug in there is another floppy drive from another PowerBook. (PB150 needs manual inject, btw, such as those used in PowerPC 'Books) The interface has absolutely nothing in common with IDE, or even the PC floppy drive interface. As JRL said, its an Apple-only standard, never used by anyone apart from Apple.