Adapting CSS for use in IE6 - works well in IE7, Mozilla

Have been adapting a perfectly good CSS (working well in IE7, Mozilla, and Safari) to IE6. Have made some progress with margins and padding but I seem to be stuck positioning my third column properly.

At this point I'm just hacking.  Some advice would be helpful

view the site at www.gtxm.com

I am using javascript to identify a browser level below IE7.

here is the IE6 adaptation to the core CSS.

/*IE 6 change ********** changed col_right margin-left to 1px */
.col_right {
      float: left;
      width: 48%;
      margin-left: 1px;
}

/* ----------------------------- COLUMN_LEFT ----------------------------- */
/*IE 6 change ********** - changed padding_left to 6px ---- */
#column_left {
      background: url(../images/bg_content.gif) repeat-x top center;
      width: 189px;
      float: left;
      padding-top: 12px;
      padding-left: 6px;
}

/* ----------------------------- COLUMN_CENTRAL ----------------------------- */
/*IE 6 change ********** - changed padding_right to 1px and added margin-left to -15 ---- */
#column_central {
      background: url(../images/bg_content.gif) repeat-x top center;
      width: 543px;
      float: left;
      min-height: 700px;
      padding-top: 10px;
      padding-right: 1px;
      margin-left: -15px;
}

/* ----------------------------- COLUMN_RIGHT ----------------------------- */
/*IE 6 change ********** - changed padding to 0px
removed float:right and added specific margins ---- */
#column_right {
      background: url(../images/bg_column_right.gif) repeat-x top center;
      width: 177px;
      padding: 0px;
      font: 10px Geneva, Verdana, Arial, Helvetica, sans-serif;
      margin-left: 729px;
      margin-right: 907px;
      margin-top: 150px;
}
html>body #column_right {
      width: 153px;
}
#column_right a {
      color: #7492b3;
}
#column_right span.a {
      color: #999;
}
#column_right h3 {
      font: 10pt Geneva, Verdana, Arial, Helvetica, sans-serif;
      font-weight: bold;
      margin-bottom: 8px;
      text-align: center;
      
}
/* ----------------------------- FORM_2COLUMN and other form controls ----------------------------- */
.form_2column label {
      width: 150px;
      display: block;
      float: left;
      text-align: right;
      margin-top: 4px;
}
.form_2column input, .form_2column select {
/* --      margin-top: 4px;  I killed this line to fix the RadCombobox vertical alignment problem - */
      margin-left: 8px;
}
.form_2column td input, .form_2column td select {
      margin-left: 0px;
}

.nofloat label {
      width: auto !important;
}
label.nofloat {
      float: none;
      display: inline;
}

input.field, select, textarea {
   font: 8pt Geneva, Verdana, Arial, Helvetica, sans-serif;
   border: 1px solid #7492b3;
   padding: 2px;
}
input:hover.field, select:hover, textarea:hover {
      background-color: #eee;
}
input:focus.field, texarea:focus {
      background-color: #eee;
}
input.field {
      width: 200px;
}
#edit_registry fieldset#event_promoter_contact_information input.field {
      width: 160px;
}

select:focus, textarea:focus {
      background-color: white;
}

label.disabled {
      color: #999;
}
input.disabled, textarea.disabled {
      background-color: white;
      border-color: #999;
}
input:hover.disabled, texarea:hover.disabled {
      background-color: white !important;
}

option {
   padding: 1px;
}
span.checkbox input {
      margin-right: 4px;
}
input.button {
      color: white;
      text-align: center;
      font-weight: bold;
      border: 0px;
      width: 100px;
      height: 28px;
      background: url(../images/button_blue.gif) top left no-repeat;
      cursor: pointer;
      font-family: Geneva, Verdana, Arial, Helvetica, sans-serif;
      font-size: 13px;
}
input.secondary {
      background: url(../images/button_gray.gif) top left no-repeat;
}
input:hover.button {
      color: #a4c2e3;
}
input:hover.secondary {
      color: #ccc;
}
fieldset {
      border: 1px solid #aaa;
      padding: 10px;  /* padding in fieldset support spotty in IE */
      margin: 0;
      background: #e7e7e7 url(../images/bg_orange_fieldset.jpg) repeat-x;
}

fieldset legend {
      font-weight: bold;
      color: #666;
      font-size: 1.1em; /* bump up legend font size, not too large or it'll overwrite border on left
                         be careful with padding, as it'll shift the nice offset on top of border  */
}
.error_message {
      color: #a00;
}

.required {
      font-size: 80%;
      color: #a00;
}
p.required {
      margin-bottom: 10px;
      text-align: right;
}

.symbol {
}

.login label {
      width: 100px;
      text-align: left;
}

#edit_preferences label {
      width: 130px;
}
#edit_preferences .settings label {
      width: 100px;
}
#select_role label {
      width: 100px;
}
#edit_preferences select {
      margin-bottom: 4px;
}

#radbutton input{
      margin-right: .3em;
      margin-left: 150px;
      float: left;      
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