Hi,
1) RS485 is, as far as I know, an electrical specification (voltage swing, drive capability of the driver chip etc) for multipoint communication, not a protocol. PBP has various built in routines for serial communications. What you do with that signal once it leaves the PIC chip is up to you. (Connect it to a RS485 transmitter for example).

2) Yes and yes. The list of supported chips can be found here: http://www.melabs.com/products/pbp.htm Start (and IMO continue...) with the 16F877 since it's a flash part. The 16C65 is either UV eraseable or an OTP part so developing code on that one will be quite a struggle.

Have a look at MELABS site and browse this forum for a information, there's lots of it. Then start slow with the standard blink-a-led and Hello World programs. Make sure to read the PBP manual and the datasheet for the PIC you are using. If you find yourself in trouble there's lots of people here to help with the specifics.

/Henrik Olsson.