[wvxvw]

Я не уверен, существует ли у LoadVars ограничение на длину передаваемой строки, но, чтобы не эксперементировать - грузил бы как XML с использованием CData.

var _xml:XML = new XML();
_xml.ignoreWhite = true;
var url_str:String = "text.xml";
var _txt:TextField = _root.createTextField("_txt", 0, 0, 0, Stage.width, Stage.height);
_txt.condenseWhite = true;
_txt.html = true;
_txt.wordWrap = true;
_txt.multiline = true;
_xml.onLoad = function(ok:Boolean):Boolean  {
	if (ok) {
		if (this.status != 0) {
			var errorMessage:String = "";
			switch (this.status) {
				case 0 :
					errorMessage = "No error; parse was completed successfully.";
					break;
				case -2 :
					errorMessage = "A CDATA section was not properly terminated.";
					break;
				case -3 :
					errorMessage = "The XML declaration was not properly terminated.";
					break;
				case -4 :
					errorMessage = "The DOCTYPE declaration was not properly terminated.";
					break;
				case -5 :
					errorMessage = "A comment was not properly terminated.";
					break;
				case -6 :
					errorMessage = "An XML element was malformed.";
					break;
				case -7 :
					errorMessage = "Out of memory.";
					break;
				case -8 :
					errorMessage = "An attribute value was not properly terminated.";
					break;
				case -9 :
					errorMessage = "A start-tag was not matched with an end-tag.";
					break;
				case -10 :
					errorMessage = "An end-tag was encountered without a matching start-tag.";
					break;
				default :
					errorMessage = "An unknown error has occurred.";
					break;
			}
			throw new Error("Error parsing XML, status: "+this.status+" ("+errorMessage+")");
		}
		afterOnLoad(this);
		return true;
	} else {
		throw new Error("There was the problem loading XML from: "+url_str);
		return false;
	}
};
function afterOnLoad(xml:XML):Void {
	_txt.htmlText = xml.childNodes[0].childNodes[0].nodeValue;
}
_xml.load(url_str);

ХМЛ для примера:

<MyLongText>
	<![CDATA[
	<p><font size='20' face='_sans'>Here goes my preformated <font color='#008888'><b>HTML</b></font> text</font></p>
	]]>
</MyLongText>