you dont really even have to go that far, a few transistors wired the right way will get at least 9600 baud (or better if you build it right) the shifter I am using now is based on a 7404 hex inverter, and handles upto 115k, but is a bit weird after that, and thats handling a real rs232 port running at 24v pp down to 3-5v logic

or you could go all nutty and use a maxium max232, which is really overkill, and kind of expensive when compared to a 7 cent 74xxXX ic