<fieldset class="formFieldset">
<legend>{global:formtitle}</legend>
{error}
<!-- Do not remove this ID, it is used to identify the page so that the pagination script can work correctly -->
<div class="section group">
<div class="col span_1_of_2">
<ol class="formContainer" id="rsform_5_page_0">
<h3>column 1</h3>
 <li class="rsform-block rsform-block-firstname">
  <div class="formBody">{FirstName:body}<span class="formClr">{FirstName:validation}</span></div>
 </li>
 <li class="rsform-block rsform-block-lastname">
  <div class="formBody">{LastName:body}<span class="formClr">{LastName:validation}</span></div>
 </li>
 <li class="rsform-block rsform-block-email">
  <div class="formBody">{Email:body}<span class="formClr">{Email:validation}</span></div>
 </li>
</ol>
</div>
<div class="col span_1_of_2">
<ol class="formContainer">
<h3>column 2</h3>
 <li class="rsform-block rsform-block-captcha">
  <div class="formBody">{Captcha:body}<span class="formClr">{Captcha:validation}</span></div>
 </li>
 <li class="rsform-block rsform-block-verzend">
  <div class="formBody">{verzend:body}<span class="formClr">{verzend:validation}</span></div>
 </li>
</ol>
</fieldset>
</div>
</div>





 Here is the CSS
===========================

/*  GRID OF TWO   ============================================================================= */
 
/*  SECTIONS  ============================================================================= */
 
.section {
 clear: both;
 padding: 0px;
 margin: 0px;
}
 
/*  GROUPING  ============================================================================= */
 
 
.group:before,
.group:after {
    content:"";
    display:table;
}
.group:after {
    clear:both;
}
.group {
    zoom:1; /* For IE 6/7 (trigger hasLayout) */
}
 
/*  GRID COLUMN SETUP   ==================================================================== */
 
.col {
 display: block;
 float:left;
 margin: 1% 0 1% 1.6%;
}
 
.col:first-child { margin-left: 0; } /* all browsers except IE6 and lower */
 
 
/*  REMOVE MARGINS AS ALL GO FULL WIDTH AT 480 PIXELS */
 
@media only screen and (max-width: 480px) {
 .col { 
  margin: 1% 0 1% 0%;
 }
}
 
.span_2_of_2 {
 width: 100%;
}
 
.span_1_of_2 {
 width: 49.2%;
}
 
/*  GO FULL WIDTH AT LESS THAN 480 PIXELS */
 
@media only screen and (max-width: 480px) {
 .span_2_of_2 {
  width: 100%; 
 }
 .span_1_of_2 {
  width: 100%; 
 }
}

To make your form more beautiful add this extra css
=====================================================
select, textarea, input[type="text"], input[type="password"], input[type="url"], input[type="email"] {
    -moz-border-bottom-colors: none;
    -moz-border-left-colors: none;
    -moz-border-right-colors: none;
    -moz-border-top-colors: none;
    border-color: #ccc #e7e7e7 #e7e7e7;
    border-image: none;
    border-right: 1px solid #e7e7e7;
    border-style: solid;
    border-width: 1px;
    box-sizing: border-box;
    color: #555;
    font-size: 14px;
    height: 36px;
    line-height: 37px;
    max-width: 100% !important;
    padding: 0 12px;
}


button, .button, input.button, span.button, button.button, div.button, input[type="submit"], input[type="button"], .pagenav-prev a, .pagenav-next a {
    background: none repeat scroll 0 0 #e89e44;
    border: medium none;
    border-radius: 2px;
    color: #fff;
    cursor: pointer;
    display: inline-block;
    font-size: 12px;
    font-weight: 600;
    height: 34px;
    line-height: 35px;
    margin: 0 5px 2px 2px;
    padding: 0 11px;
    text-align: center;
    text-transform: uppercase;
    transition: background-color 0.12s ease-out 0s;
}