CSS - Ie7 'bump' Bug

I have finally got my page set up as required. There is one minor niggle.

The footer sits at the bottom of the page when the browser is maximised and has no content. If the browser is not maximised or the content introduces scroll bars the footer is bumped up one pixel in IE. How can I get around this? The footer CSS is below, if you require any more CSS let me know which elements (roughly) as there is a lot of it.

PHP Code:
#wrap {
     margin-left: auto; /*center the wrapper CSS2 compliant (all except IE*/
     margin-right: auto;
     margin-top: -21px;
     width: 760px;
     top: 21px;
     min-height: 100%;
     position: relative;
     left: 0px;
     background-image: url(../images/content_bg.gif);
     text-align: left;
     
}

* html #wrap {
     height:100%;
     padding-bottom: -20px;
}

#clear_footer {
     clear: both;
     height: 21px;
     overflow: visible;
     z-index: 1999;
     /*background-color: green; Used for demonstration purposes only, remove after testing*/
}

#contain_footer {
     left: 0;
     margin-top: -21px;
     width: 100%;
     height: 21px;
     background-color: red;
     background-image: url(../images/contain_footer_bg.gif);
     padding-bottom: 0px;
     z-index: 2002;
}

#footer {
    position: absolute;
    bottom: 0;
    margin: 0 auto;
    width: 760px;
    height: 21px;
    line-height: 21px;
    vertical-align: center;
    background-image: url(../images/footer_bg.gif);
    z-index: 1999;
} 

I have a very simple form that has a select list and next to it a submit button. If I use a standard button for the submit then it sits next to the select list (on the right of it). If I change the submit button to an image it pushes the select list down by about 5 pixels.

I have tried everything I can think of, everything is set to display:inline etc but I can't work out the problem.

Any ideas? It happens on firefox and IE6 and probably all other browsers as well.