What is the difference between Intel and PPC? What is the hardware and software differences between Intel and PPC Macs?
Hardware-wise: PowerPC is a microprocessor developed mainly by the three developing companies Apple, IBM, and Motorola. It is built with reduced instruction-set computer (RISC) which speeds-up the operation of MIPS (million instructions per second). PowerPC is mainly based on IBM’s earlier Power architecture because it has a similar RISC instruction set for microprocessors.

Intel and AMD CPU's are based on CISC architectures. Typically CISC chips have a large amount of different and complex instructions. The philosophy behind it is that hardware is always faster than software, therefore one should make a powerful instructionset, which provides programmers with assembly instructions to do a lot with short programs.
In common CISC chips are relatively slow (compared to RISC chips) per instruction, but use little (less than RISC) instruction