Basic Twitter object, demo at the bottom (require jQuery here but could also write your own Ajax function). This should work w/ all Twitter APIs which do not require authentification.

gistfile1.js

// Extending the JS Object (not really advised in theory but we really need this to know an associative array size)
Object.prototype.size = function () {
  var len = this.length ? --this.length : -1;
    for (var k in this)
      len++;
  return len;
};

// Twitter class
function Twitter() {
  this.base_url = 'http://api.twitter.com';
  this.version = 1;
  
  /**
   * Make an API call and get the result w/ a callback
   *
   * @param settings mixed type (associative array) containing the informations to build the API call (see demo)
   * @param callback function
   *
   */
  Twitter.prototype.api = function(settings, callback) {
    // Generate the basic API URI
    var api_uri = this.base_url + '/' + this.version + '/' + settings.api + '/' + settings.method + '.' + settings.format;
    
    // Append parameters to the URI (if any)
    if (settings.params.size()) {
      api_uri += '?';
      for (var param in settings.params) {
        if (settings.params[param] == null || settings.params[param] == false || settings.param == 'size')
          continue;
          
        api_uri += param + '=' + settings.params[param] + '&';
      }
    }
    
    // Perform an Ajax request (using jQuery here but could be something else, also jQuery requires the format to be JSONP)
    jQuery.getJSON(api_uri + 'callback=?', callback);
  };
  
  /**
   * Take a tweet and HTMLize the content of the tweet (URIs, hashtags, @user)
   *
   * @param tweet (text) to HTMLize
   *
   */
  Twitter.prototype.htmlize_tweet = function(tweet) {
    // replace url w/ links
    tweet = tweet.replace(/(\b(https?|ftp|file):\/\/[-A-Z0-9+&@#\/%?=~_|!:,.;]*[-A-Z0-9+&@#\/%=~_|])/gi, '<a href="$&" target="_blank">$&</a>');
    // replace hashtags w/ links
    tweet = tweet.replace(/#(\w+)/g, '<a href="http://search.twitter.com/search?q=%23$1" target="_blank">#$1</a>');
    // replace @username w/ links
    tweet = tweet.replace(/@(\w+)/g, '<a href="http://twitter.com/$1" target="_blank">@$1</a>');
    // return HTMLized tweet
    return tweet;
  };
  
  /**
   * Calculate how old a tweet is
   *
   * @param timestamp (Date object) which is in theory right now but could also be some other date in the future (past is not advised for obvious reasons)
   * @param tweet creation time (also a Date object)
   *
   */
  Twitter.prototype.time_string = function(timestamp, created_at) {
    // Time constants
    var second = 1000;
    var minute = second * 60;
    var hour = minute * 60;
    var day = hour * 24;
    var week = day * 7;
    
    // Timediff
    timediff = timestamp - created_at;
    
    // Create timestring
    if (timediff < second * 7)
      return 'right now';
    if (timediff < minute)
      return Math.floor(timediff / second) + ' seconds ago';
    if (timediff < minute * 2)
      return 'about a minute ago';
    if (timediff < hour)
      return Math.floor(timediff / minute) + ' minutes ago';
    if (timediff < hour * 2)
      return 'about an hour ago';
    if (timediff < day)
      return Math.floor(timediff / hour) + ' hours ago';
    if (timediff > day && timediff < day * 2)
      return 'yesterday';
    if (timediff < day * 365)
      return Math.floor(timediff / day) + ' days ago';
    else
      return 'over a year ago';
  };
};