Salesforce REST API Login?

What you're describing, sounds like OAuth (just because you mention access-token).

There's a good example of OAuth being used in Salesforce below...

http://wiki.developerforce.com/page/Digging_Deeper_into_OAuth_2.0_at_Salesforce.com

SOLUTION:

Hi all, I have arrived the solution to my problem. Actually, I was examining the sample given in the link http://wiki.developerforce.com/page/Getting_Started_with_the_Force.com_REST_API . Then implemented OAuth 2.0 Username-Password Flow which is from https://login.salesforce.com/help/doc/en/remoteaccess_oauth_username_password_flow.htm#send_up_response. It solves my problem.