Hi karthik,

I saw your code,I have couple of questions,I hope you can help me.

1) The below given code will be used by client aplication which is running outside salesforce.Is that correct?

2) Now from where do we get the following information.

3) Do we have to specify a paritcular username and passowrd Which will always remain?

4) Once we get the access token thenhow do we use that ?.Can u please help.

    -grant_type=password'

    client_id=' + client_id +

    client_secret=' + client_secret + '

    username=' + EncodingUtil.urlEncode(username, 'UTF-8') 

    password=' + EncodingUtil.urlEncode(password,.'UTF-8')

Try using  Obtaining a Token in an Autonomous Client (Username-Password Flow)

By setting the grant_type=password.

Httprequest req = new HttpRequest();		
		req.setMethod('POST');		
		req.setHeader('Content-Type','application/x-www-form-urlencoded');		
		req.setBody('grant_type=password' + 
					'&client_id=' + client_id + 
					'&client_secret=' + client_secret + 
					'&username=' + EncodingUtil.urlEncode(username, 'UTF-8') + 
					'&password=' + EncodingUtil.urlEncode(password, 'UTF-8')); 		
		req.setEndpoint(OAuthURL);			
    	
    	Http http = new Http();
		HttpResponse res;
		
		try {
			
			if(!Test.isRunningTest())
				res = http.send(req);
			else
				return null;
					
		}catch(system.CalloutException e){
			ApexPages.addMessage(new ApexPages.Message(ApexPages.Severity.ERROR, e.getMessage()));
			return null;
		}

The response will contain the Access Token.