頼まれたのでswfTagWriter.jsの書き出しに必要な部分だけをパクりつつ、リファクターしてみたよ。使うのはこんな感じ：

  var f = Flash.TagWriter({
     filename: '/path/to/flash.swf',
     attributes: { some_html_attribute: 'hoge' },
     flashvars: { var1: 'value' },
     parameters: { param1: 'param1' },
     width: 720,
     height: 50,
     id: 'my_id',
     loop: false,
     quality: 'high'
  });
  document.write(f);

使えそうだったらどうぞー。

  if (typeof Class == 'undefined') {
    Class = {
      create: function() {
        return function() { this.initialize.apply(this, arguments) };
      }
    };
  }
  var Flash = {};

  (function() {
    Flash.Detector  = Class.create();
    Flash.TagWriter = Class.create();

    Flash.Util = {};
    Flash.Util.htmlEscape = function(string) {
      string = '' + string; /* force stringification */
      return string.replace(/&/g, '&#38;').replace(/</g, '&#60;').replace(/>/g, '&#62;');
    }

    Flash.Detector.prototype = {
      initialize: function() {
      },
      isAvailable: function() {
        if (navigator.plugins && navigator.mimeTypes.length > 0 && navigator.plugins["Shockwave Flash"]) {
          return true;
        }

        var ret = false;
        if (window.ActiveXObject) { /* Oh, the gory */
          /*@cc_on
          @if(@_jscript_version >= 5.0)
          try {
            var player = new ActiveXObject("ShockwaveFlash.ShockwaveFlash");
            ret = true;
          } catch(e) {}
          @end @*/
        }
        return ret;
      }
    };

    Flash.TagWriter.prototype = {
      initialize: function(opts) {
        if (opts == null) opts = {};
        var member = {
          attributes: {},
          flashvars: {},
          parameters: {},
          filename: '',
          width: '',
          height: '',
          id: '',
          loop: false,
          quality: 'high'
        };
        for(var key in member) {
          this[key] = opts[key] || member[key];
        }

        var detector = new Flash.Detector();
        this.html = 
          detector.isAvailable() ?
            ( this.isMSIE() ? this.htmlForMSIE : this.htmlForSaneBrowsers ) :
            this.htmlForNonFlash
        ;
      },
      isMSIE: function() {
        var agent = navigator.userAgent.toLowerCase();
        return (
          agent.indexOf('msie')  >=  0 &&
          agent.indexOf('win')   >=  0 &&
          agent.indexOf('opera') == -1 
        ) ;
      },
      htmlForMSIE: function() {
        var html = '';
        html += 
          '<object ' +
          'classid="clsid:D27CDB6E-AE6D-11cf-96B8-444553540000" ' +
          'codebase="http://download.macromedia.com/pub/shockwave/cabs/flash/swflash.cab#' + '" ' 
          'width="'  + this.width + '" ' +
          'height="' + this.height + '" ' +
          'id="'     + this.id + '" '
        ;
        html += ">\n";
        html += this.htmlForParams();
        html += this.htmlForFlashVars();
        html += "</object>\n";
        return html;
      },
      htmlForSaneBrowsers: function() {
        var html = '';

        html +=
          '<object ' +
          'type="application/x-shockwave-flash" ' +
          'data="'   + this.filename + '" ' +
          'width="'  + this.width + '" ' +
          'height="' + this.height + '" ' +
          'id="'     + this.id + '" '
        ;
        html += ">\n";
        html += this.htmlForParams();
        html += this.htmlForFlashVars();
        html += "</object>\n";
        return html;
      },
      htmlForNonFlash: function() {
        return '<p>You have to <a href="http://www.macromedia.com/jp/shockwave/download/?P1_Prod_Version=ShockwaveFlash&#38;Lang=Japanese">install or update Flash Player</a> in order to display the content.</p>';
      },
      htmlForParams: function() {
        var html = '';
        var params = {};
        for(var key in this.parameters) {
          params[key] = this.parameters[key];
        }
        params.movie   = this.filename;
        params.loop    = this.loop;
        params.quality = this.quality;

        for(var key in params) {
          html += '<param name="' + key + '" value="' + Flash.Util.htmlEscape(params[key]) + "\" />\n";
        }
        return html;
      },
      htmlForFlashVars: function() {
        var varlist = [];
        for(var key in this.flashvars) {
          varlist.push(
            key + '=' + Flash.Util.htmlEscape(this.flashvars[key])
          );
        }

        return (varlist.length > 0) ?
          '<param name="flashvars" value="' + varlist.join('&') + "\" />\n" :
          ''
        ;
      },
      htmlForAttributes: function() {
        var html = '';
        for (var key in this.attributes) {
          var value = "" + this.attributes[key];
          html += key + '="' + Flash.Util.htmlEscape(value) + '" ';
        }
        return html;
      }
    };
  })();