My first JavaScript. Any errors?
<p>Good Sunday morning!</p>

<p>After fiddling around with some JavaScript this weekend, I finally wrote my first script. It is a Tooltip generator. It works great in FF 3 + 3.5, IE 6 + 7, Safari 4, Chrome 2 + 3, and Opera 9 + 10.</p>

<p>Before putting my new code into production, I thought I'd ask if you see any glaring problems -- or maybe it's perfect as-is? (Lol)</p>

<p>JSLint.com reports:</p>

<pre><code>Error:

Problem at line 10 character 15: 'e' is already defined.

    var e = window.event;

Implied global: window 10, document 19,20,22,24,33,35,41,43,49,55
</code></pre>

<p>Here is my code (apologies in advance if you don't like my code style):</p>

<pre><code>function getmouseposition( e )
{
    var offx = 22;
    var offy = 14;
    var posx = 0;
    var posy = 0;

    if ( !e )
    {
     var e = window.event;
    }
    if ( e.pageX || e.pageY )
    {
     posx = e.pageX;
     posy = e.pageY;
    }
    else if ( e.clientX || e.clientY )
    {
     posx = e.clientX
               + document.body.scrollLeft
               + document.documentElement.scrollLeft;
     posy = e.clientY
               + document.body.scrollTop
               + document.documentElement.scrollTop;
    }
    if ( document.getElementById )
    {
     var tooltip = document.getElementById( 'tooltip' );

     tooltip.style.left = ( posx + offx ) + 'px';
     tooltip.style.top = ( posy + offy ) + 'px';
    }
}

function tooltip_on( text )
{
    if( !document.getElementById( 'tooltip' ) )
    {
     var span = document.createElement( 'span' );

     span.id = 'tooltip';
     span.style.display = 'none';
     span.innerHTML = '&amp;nbsp;';

     document.body.appendChild( span );
    }
    var tooltip = document.getElementById( 'tooltip' );

    tooltip.innerHTML = text;
    tooltip.style.display = 'block';
    tooltip.style.position = 'absolute';

    document.onmouseover = getmouseposition;
    // document.onmousemove = getmouseposition;
}

function tooltip_off()
{
    document.getElementById( 'tooltip' ).style.display = 'none';
}
</code></pre>

<p>EDIT:</p>

<p>I'm also wondering, what does this line say (in layman's terms ) in the <code>getmouseposition function</code>:</p>

<pre><code>if ( document.getElementById )
</code></pre>
