1.plz tell me the steps of installing FreeRADIUS on Linux 7.3
2.and also tell me how to configure it for MD5 and EAP.
3.how to use freeRADIUS within our C program

You install it like many apps. Get the source and then:

./configure
make
make install

You configure it by modifying a number of different config files. My install put them into /usr/local/etc/raddb. You can configure it to authenticate usernames and passwords from a number of different "realms" including users on your Linux system, or from a mysql server. I'm not quite sure what you mean by configuring it for MD5, though...

As for using it from a C program, I seem to recall there being some libraries with it, but I really haven't looked at any sort of API to interface with it. FreeRADIUS itself is a RADIUS server, so I'm not quite sure what it is you want to do to "use" it from a C program? Do you mean you want to send RADIUS authentication requests to it from your program? If that is the case, one option would be to look at the RFC. (I don't have the number offhand, do a Google search.) The RADIUS protocol is not too complex.

The best thing for more information on FreeRADIUS might be to check out the development lists for it. My own limitted knowledge of it comes from setting it up to authenticate requests from a Cisco Access Server. And I wrote a small RADIUS client to send it requests for testing purposes. I just went right to the RFC and did my test app from scratch, though.

If you need to check for error logs, FreeRADIUS logs to /usr/local/var/log/radius. You can also configure it to log all requests and responses for debugging.

Dear!
i am very thankfull to you because you have guided me even i have put worng questions.
dear i want to know details of writing client for the freeRADIUS and i hope that you will tell me more details about writing client (development details)
i have now installed freeRADIUS successfully , plz now tell what next step i have to perform, i dont know how to use it now. plz help me out.
thank you in anticipation.

There are a number of ways you can use it. As I stated in my other post the basic RADIUS protocol is defined in RFC 2865 and the accounting stuff is defined in RFC 2866. There are also a number of RFCs that define various extensions, but 2865 should be all you need to start with. To understand the protocol, you really need to understand how to work with data on the byte and bit level, though.

Also, a lot of access points have built-in support for the RADIUS protocol, and just have to be configured appropriately.

My knowledge of RADIUS comes from the fact that we setup a Cisco Access Server to use RADIUS for authentication on inbound, and outbound calls. We wrote our own little prototype RADIUS server for this, and used FreeRADIUS as a backup to verify that we were sending back packets appropriately. I also wrote a simple RADIUS client that we used for testing the server prototype. The code I wrote is in C#, since that's what we use in our work environment, though.