Doctype zerstört Javascript ?!?

[Arcteryx]

Hallo Leute,

ich komme nicht weiter, ich habe mir einen Tooltip zusammengeschustert, der hat auch wunderbar funktioniert...nur wenn ich jetzt ein Doctype festlege, reagiert der Tooltip anders. Sprich es wird nicht mehr an der richtigen Stelle dargestellt. Im FF folgt er zwar der Maus, liegt jedoch ganz oben am Browserrand, bei y=0px. Im IE ändert sich der y-Wert je nachdem, wo man gerade hinscrollt. Kann mir jemand helfen bzw. mir sagen, wo der Fehler liegt? Vielen Dank!

Hier mein Javascript:

var OP = (navigator.userAgent.indexOf('Opera') != -1) ? true : false;
  var IE = (navigator.userAgent.indexOf('MSIE') != -1 && !OP) ? true : false;
  var GK = (navigator.userAgent.indexOf('Gecko') != -1) ? true : false;
  var NN4 = document.layers;
  var DOM = document.getElementById;

function TOOLTIP() {

this.width = 150;                     // width (pixels)
    this.bgColor = '#FFFFFF';             // background color
    this.textColor = '#2f2f2f';           // text color
    this.borderColor = '#5d5d5d';         // border color
    this.opacity = 100;                    // opacity (percent) - doesn't work with all browsers
    this.cursorDistance = -70;              // distance from cursor (pixels)

// don't change
    this.text = '';
    this.height = 0;
    this.obj = 0;
    this.sobj = 0;
    this.active = false;

this.create = function() {
      if(!this.sobj) this.init();

var t = '<div id="datumhover">' + this.text + '</div>';

if(NN4) {
        t = '<div id="datumhover">' + this.text + '</div>';
        this.sobj.document.write(t);
        this.sobj.document.close();
      }
      else {
        this.sobj.border = '0px' + this.borderColor;
        this.setOpacity();
        if(document.getElementById) document.getElementById('ToolTip').innerHTML = t;
        else document.all.ToolTip.innerHTML = t;
      }
      if(DOM) this.height = this.obj.offsetHeight;
      else if(IE) this.height = this.sobj.pixelHeight;
      else if(NN4) this.height = this.obj.clip.bottom;

this.show();
    }

this.init = function() {
      if(DOM) {
        this.obj = document.getElementById('ToolTip');
        this.sobj = this.obj.style;
      }
      else if(IE) {
        this.obj = document.all.ToolTip;
        this.sobj = this.obj.style;
      }
      else if(NN4) {
        this.obj = document.ToolTip;
        this.sobj = this.obj;
      }
    }

this.show = function() {
      var ext = (document.layers ? '' : 'px');
      var left = mouseX;
      var top = mouseY;

if(left + this.width + this.cursorDistance > winX) left -= this.width + this.cursorDistance;
      else left += this.cursorDistance;

if(top + this.height + this.cursorDistance - scrTop > winY) top -= this.height;
      else top += this.cursorDistance;

this.sobj.left = left + ext;
      this.sobj.top = top + 35;

if(!this.active) {
        this.sobj.visibility = 'visible';
        this.active = true;
      }
    }

this.hide = function() {
      if(this.sobj) this.sobj.visibility = 'hidden';
      this.active = false;
    }

this.setOpacity = function() {
      this.sobj.filter = 'alpha(opacity=' + this.opacity + ')';
      this.sobj.mozOpacity = '.1';
      if(this.obj.filters) this.obj.filters.alpha.opacity = this.opacity;
      if(!document.all && this.sobj.setProperty) this.sobj.setProperty('-moz-opacity', this.opacity / 100, '');
    }
  }

var tooltip = mouseX = mouseY = winX = winY = scrTop = 0;

if(document.layers) {
    document.write('<layer id="ToolTip"></layer>');
    document.captureEvents(Event.MOUSEMOVE);
  }
  else document.write('<div id="ToolTip" style="position:absolute; z-index:69;"></div>');
  document.onmousemove = getMouseXY;

function getMouseXY(e) {
    if(document.body && document.body.scrollTop >= 0) scrTop = document.body.scrollTop;
    else if(window.pageYOffset >= 0) scrTop = window.pageYOffset;

if(IE) {
      mouseX = event.clientX + document.body.scrollLeft;
      mouseY = event.clientY + document.body.scrollTop;
    }
    else {
      mouseX = e.pageX;
      mouseY = e.pageY;
    }

if(mouseX < 0) mouseX = 0;
    if(mouseY < 0) mouseY = 0;

if(GK || NN4) {
      winX = window.innerWidth - 25;
      winY = window.innerHeight;
    }
    else if(DOM) {
      winX = document.body.offsetWidth - 25;
      winY = document.body.offsetHeight;
    }
    else {
      winX = screen.width - 25;
      winY = screen.height;
    }
    if(tooltip && tooltip.active) tooltip.show();
  }

function toolTip(text, width, opacity) {
    if(text) {
      tooltip = new TOOLTIP();
      tooltip.text = text;
      if(width) tooltip.width = width;
      if(opacity) tooltip.opacity = opacity;
      tooltip.create();
    }
    else if(tooltip) tooltip.hide();
  }