May I just use space (that is, Serial.write(040)) to be the seperator?
As long as you can ensure that the high order byte and the low order byte of any integer will never be 32, 0x20, 040, you can.
Of course, I don't see how you can ensure that, given that the values come from accelerometer data.
Is there any reason that the data can't be logged locally, and displayed later? This would be far faster than trying to send data over the serial port.