Mike,
You might consider using a pair of 2N7000 or BS170 MOSFETs... They use practically no power and work extremely well with those otherwise troublesome low-voltage PC/Laptop ports... They're also open-drain and will "pull-up" to whatever voltage you want (within reason, grin)...
Here's the circuit I use -- two 2N7000's and two resistors... I've used it without problem on many different PCs and laptops with baud rates up to 115,200 baud... While the circuit as drawn shows a resistor on the PIC board and two transistors and a resistor built into a DB9F shell with 3.5mm stereo plug and jack connections, all four components can easily be installed on the PIC board along with a DB9F connector...
Regards, Mike