Download the dll and use this code
protected void btnPostTweet_Click(object sender, EventArgs e)
{
OAuthTokens tokens = new OAuthTokens();
tokens.AccessToken = “xxxxxxxx”;
tokens.AccessTokenSecret = “xxxxxx”;
tokens.ConsumerKey = “xxxxxx”;
tokens.ConsumerSecret = “xxxxxx”;
var tweetResponse = TwitterStatus.Update(tokens, "Hello, #Twitterizer");
if (tweetResponse.Result == RequestResult.Success)
{
// Tweet posted successfully!
}
else
{
// Something bad happened
}
}