input[type=text]{
    width:348px;
    height:30px;
    border:1px solid #ddd;
    padding:3px;
    background:url(../img/formfieldbg.gif) repeat-x;
    -moz-border-radius: 5px;
    -webkit-border-radius: 5px;
    border-radius: 5px;
    vertical-align:top;
    behavior: url(path/to/PIE.htc);}

behavior: url(/path/to/PIE.htc);

behavior: url(//example.com/path/to/PIE.htc);