Hi,
driving both sides of the transducer alternatively will give you 2xVdd bipolar signal but make sure the xducer terminals are floating. I am assuming it's 40kHz unit - these present a high capacitance load and am not sure PIC can give you enough drive to get the full Vdd amplitude. Hopefully you don't have any tuning inductor across the xducer..

Like Steve says, use couple of transistors to buffer the PIC output.

As for code - you are looking at 12.5usec pulsewidth -so assembly would be the way - unless Steve can help you with generating such short pulses with PBP. Remember that these have narrow tuning range (no more than 1kHz or so or Hi Q) so you don't have much room for pulsewidth variation- may be you need to use HS clock... PBP, as far as I know, can only put out pulses in 1usec interval (pauseus) so you have to use 12usec for pulses and 1usec in between. And to get good acoustic power out you need a burst of few cycles ....

-warrier