If you dont already have it, all the info you will need is in the data sheet:

http://www.magnevation.com/pdfs/speakjetusermanual.pdf

You can interface with the chip using serial communication from a PIC. SpeakJet's pin 10 (RCX) is a serial input (TTL). Connect your pic like this:

Code:
PIC I/O Pin --------+------- SpeakJet Pin 10
                    |
                   ---
                   | | 47k Resistor
                   | |
                   ---
                    |
                  Ground
You can use pbp's SEROUT routine to communicate with the chip.

The default baud rate for the SpeakJet chip is 9600, but can be changed. I dont see any need to deviate from the default tho.

I recommend your read the chips data sheet if you havnt already.