I have tried to install 56kbps extenal modem in Open Linux. But Modem is not at all responding. Even I tried with minicom tool The error message i got is dev/ttys0 input/ output error. and i want to know how should I configure my modem and My dial up networking. and How should I dial after configuring my modem.
If any body knows answer to my question please reply back. I will be very much thankful to them.

Don't know much about Open Linux (I'm a RHAT user, myself), but in general, there are three things that determine your modem connection:

serial port settings in the motherboard
serial port settings in the OS
Modem settings

First I would make sure that you have your serial port turned on in the BIOS. If you don't know how to do this, I am uncomfortable doing it with you in a forum environment. Try and find a friend who can help you with it.

If the serial port is configured properly on the motherboard, you can check the serial port settings in the OS with the setserial /dev/ttyS0 and make sure that alll the settings match the hardware settings that your serial port should be using.

Lastly, read the doicumentation for the modem. Some external modems have different configurations from the norm. Make sure, if you need to, that you are using a null-modem cable, that it is connected to the proper port, and that the IRQs and IOs are set right. This is really what the documentation is for.

If all those check out OK and you still can't connect to the modem, try checking a hardware compatibility list of some sort for Open Linux. Many times certain hardware only works with certain versions of Linux OSes.

Hope this helps.