Hi,
Just compare the pin out of both processors:
Here's the PIC16F628

That said... From what you write, I get a feeling that you won't be able to port code from a processor core with Harvard architecture to a core with von Neumann architecture, so perhaps you would be better of modifying the PIC to send the mouse data to the AVR (via SPI, I2C or something similar) and just run both processors.