If you are new to OAuth check out http://oauth.net first. There is important details you need to know in the spec before you get started. The site also provides links to libraries for about every major language out there. Not sure if you rolled your own twitter library or what language you using.
To get the access token you just need to fetch an request token, authorize it, and then exchange it for an access token. There is not a way to automate the authorization step. You can check out this python script  which queries for your consumer key/secret then opens the authorization link in the browser. At the end you get your access token. Note: it depends on this  library. Where you go next depends on which library / language you go with. Best of luck, Josh  http://www.pastie.org/634526  http://github.com/joshthecoder/tweepy