As far as I know, com2 is not referenced as com4 as it is in windows. You do have, however, have /dev/tty2a and /dev/tty2A as two seperate devices. Remember that they occupy the same interupt and addresses, just as com2 and com4 in windows.
what exactly are you trying to do?
what is the problem you are trying to solve?
mbrown@computereaseinc.net