pranav81, it sounds like both devices are set to use COM3. You need to tell one of them to use another port. (i.e. COM4, it you're not already using that one.)
On some of the older cards, there were switches that had to be set to tell the card what COM port to use. Most of the newer ones, (i.e. Plug and Play) the COM port is set via software.
For example, to change the COM port on my current modem, I would go to the "Device Manager" (I also use XP). I would then find my modem in the list of devices, right click on it and select "Properties". Under "Advanced Port Settings" there is a drop-down menu that I can use to select the desired COM port. The device manager should also inform you if one device conflicts with another. (i.e. If you change it to COM4, but another device it using that one.)
I hope this helps. Good luck.
I used to be indecisive, but now I'm not so sure...