JavaScript to parse an HTML document and create simple Document Object Model (DOM)

I need a functions to create a DOM from a HTML document. I am experience in JavaScript but I cannot figure this out. Here is a skeleton of functions DreamweaverMX uses to create XML documents. Macromedia gives extension developers permission to use their functions and methods but I do think this will work with HTML files. Here is the functions and beneath them there are more details listing exactly what I need.

XMLDoc:
function XMLDoc(source, errFn) {
    this.topNode = null;
    this.errFn = errFn;
    this.createXMLNode = _XMLDoc_createXMLNode;
    this.error = _XMLDoc_error;
    this.getUnderlyingXMLText = _XMLDoc_getUnderlyingXMLText;
    this.handleNode = _XMLDoc_handleNode;
    this.hasErrors = false;
    this.insertNodeAfter = _XMLDoc_insertNodeAfter;
    this.insertNodeInto = _XMLDoc_insertNodeInto;
    this.parse = _XMLDoc_parse;
    this.parseAttribute = _XMLDoc_parseAttribute;
    this.parseDTD = _XMLDoc_parseDTD;
    this.parsePI = _XMLDoc_parsePI;
    this.parseTag = _XMLDoc_parseTag;
    this.removeNodeFromTree = _XMLDoc_removeNodeFromTree;
    this.replaceNodeContents = _XMLDoc_replaceNodeContents;
    this.source = source;
    if (this.parse()) {
        if (this.topNode != null) {
            return this.error("expected close " + this.topNode.tagName);
        } else {
            return true;
        }
    }
    return null;
}

_XMLDoc_parse:
function _XMLDoc_parse() {
    var pos = 0;
    err = false;
    while (!err) {
        var closing_tag_prefix = "";
        var chpos = this.source.indexOf("<", pos);
        var open_length = 1;
        var open;
        var close;
        if (chpos == -1) {
            break;
        }
        open = chpos;
        var str = this.source.substring(pos, open);
        if (str.length != 0) {
            err = !this.handleNode(new XMLNode("TEXT", this, str));
        }
        if (chpos == this.source.indexOf("<?", pos)) {
            pos = this.parsePI(this.source, pos + 2);
            if (pos == 0) {
                err = true;
            }
            continue;
        }
        if (chpos == this.source.indexOf("<!DOCTYPE", pos)) {
            pos = this.parseDTD(this.source, chpos + 9);
            if (pos == 0) {
                err = true;
            }
            continue;
        }
        if (chpos == this.source.indexOf("<!--", pos)) {
            open_length = 4;
            closing_tag_prefix = "--";
        }
        if (chpos == this.source.indexOf("<![CDATA[", pos)) {
            open_length = 9;
            closing_tag_prefix = "]]";
        }
        chpos = this.source.indexOf(closing_tag_prefix + ">", chpos);
        if (chpos == -1) {
            return this.error("expected closing tag sequence: " + closing_tag_prefix + ">");
        }
        close = chpos + closing_tag_prefix.length;
        str = this.source.substring(open + 1, close);
        var n = this.parseTag(str);
        if (n) {
            err = !this.handleNode(n);
        }
        pos = close + 1;
    }
    return !err;
}
_XMLDoc_handleNode:
function _XMLDoc_handleNode(current) {
    if ((current.nodeType == "COMMENT") && (this.topNode != null)) {
        return this.topNode.addElement(current);
    } else {
        if ((current.nodeType == "TEXT") || (current.nodeType == "CDATA")) {
            if (this.topNode == null) {
                if (trim(current.content, true, false) == "") {
                    return true;
                } else {
                    return this.error("expected document node, found: " + current);
                }
            } else {
                return this.topNode.addElement(current);
            }
        } else {
            if ((current.nodeType == "OPEN") || (current.nodeType == "SINGLE")) {
                var success = false;
                if (this.topNode == null) {
                    this.docNode = current;
                    current.parent = null;
                    success = true;
                } else {
                    success = this.topNode.addElement(current);
                }
                if (success && (current.nodeType != "SINGLE")) {
                    this.topNode = current;
                }
                current.nodeType = "ELEMENT";
                return success;
            } else {
                if (current.nodeType == "CLOSE") {
                    if (this.topNode == null) {
                        return this.error("close tag without open: " + current.toString());
                    } else {
                        if (current.tagName != this.topNode.tagName) {
                            return this.error("expected closing " + this.topNode.tagName + ", found closing " + current.tagName);
                        } else {
                            this.topNode = this.topNode.getParent();
                        }
                    }
                }
            }
        }
    }
    return true;
}

I have only included three main functions.  The above is only used for a reference. I don't think it will work by it's self nor do I need all the extra functions it seems to have. Only the functions listed below.

I need to be able to do this:

var theDOM = new HTMLDOM(strHTML); // this builds a html document object model from a html document in a string.
var theNode = theDOM.getElementByID("sna"); // This gets the node by it's ID. eg, "<td id='sna'>some text</td>" returns a node of this td tag;
var theNode = theDOM.getNodeByIDorName("NameOrID");
var theParent = theNode.parentNode; // if tag was in
var intImgWidth = theNode.getAttribute('width');
theNode.setAttribute("align",curAlign); // sets tag attribute
theNode.removeAttribute("align",curAlign); // removes tag attribute
var tagName = theNode.tagName; // gets tagName. eg "<img src='fds.gif'>" returns "img"
var innerHTML = theNode.innerHTML(); // returns everything inside a tag. eg "<div>some text</div>" returns "some text"
var outerHTML = theNode.outerHTML(); // the same as above but with the tags included
theNode.innerHTML = "<div style='width:135'>some text</div>"; // this would set the innerHTML property
var sourceHTML = theDOM.source; // returns the whole document in the form of a string.

I dont know if this is a lot of work for an actual educated programmer. I am self-educated. If you build this from scratch and then decide to sell it then go for it. All I want is a licensed copy to include my project I dont care what you do with it. I can send you all the functions that go with this script in a separate email. You can also enumerate them in the DMX enviornment. You can do this by typing dw.getDocumentDOM().parentWindow in my script console extension I've built. Ask for it and I will send it to you. It is requires Dreamweaver MX.

Omicron Persei 8