I had a similar problem many years ago with a security system. I modified a serial port board with a different oscillator frequency and used a custom divisor for the serial chip - this was under ms-dos. May I suggest you look at the usb-serial chips (www.ftdi.com) as they has a 6mhz crystal and must perform some magic to get the normal baud rates. This magic may be able to work for you. Failing that, a dedicated box that converts the baud rates may be another solution (serial to serial buffer) - BlackBox may have something that can be modified. In Australia, Alfatron (www.alfatron.com.au) may be able to modify one of their products to suit. I've had dealings with them before and they're usually quite flexible.