yeah, I built my cable with the connector from mouser for my usb>obdII reader I built (also a pic btw, pic18f2455) I mainly built it for diagnostics and for checking my arduino up against. SO...I'll only be working on PWM, as that's the only car I have access to, BUT the code should work on VPW as well with slight modifications (vpw uses only the 1 data line instead of 2, but same logically and physically otherwise).
I have found a few more resources about it, and also, I now have a noob knowledge of how differential bus works :P. apparently, you send the signal on the bus+ line, and send the complement of that signal on the bus- line, so from what I understand, when high on bus+, you need to pull bus- low, and vice versa. If I am wrong, PLEASE correct me. Anywho, so I don't think I need any extra hardware to bit bang it, so I'll be working on functions for sending the triggers and converting the hex code to the appropriate high's and low's. Here's a little more about pwm (and vpw for that matter) for those interested:
SAE J1850 Description, Electrical Interface Bus