Izabel, Something tells me that you have to setup the serial port before you can use a driver, The serial port used by most systems is com1:
Serial ports are not like USB ports and notice when you plug something into them. You first have to activate it with a baud rate and some other commands.
Also, some 25 pin connections to your computer could be a parallel port which are normally a female 25 pin on your computer whereas serial are either 9 pin or 25 pin male ports.
What kind of cable is on your tape drive.??
is it a 25 pin? and is the plug side male or female?