The MicroChip web site has an App note describing a PIC implementation of
the Apple Desktop Bus (ADB). Note that the code can be downloaded
seperately from the PDF App note. As regards the PIC to IR there are
numerous schematics on the web for constructing simple IR transmitters and
receivers.  To make an IRDA compliant transceiver though you will would be
advised to use a Sharp or HP module. Sharp and several other companies
sell IRDA transceivers that plug into the serial ports of PCs. As regards
Mac versions, I am not sure. The Newton does have an IR transceiver. I
think the model 130 is IRDA but I am not sure.

***Disclaimer*** My advice and/or opinions: are frequently wrong and may
be hazardous to health and/or property; are my own, and in no way
represent my employer, friends or family; and may be illegal and/or
immoral in some countries.