如何用JS更改文本框的Enabled的值？急！

Question

input不支持enabled属性
<form name=form1>
<input name="ApplyCardID" type="text" value="由系统自动分配..." id="ApplyCardID" disabled="true" style="background-color:Gainsboro;width:150px;" />
<input id="ApplyCheck" type="checkbox" name="ApplyCheck" onclick="return ApplyCheckChange();" checked/>
<script language="javascript">
function ApplyCheckChange()
{
    if (document.form1.elements["ApplyCheck"].checked==true)
    {
        document.form1.elements["ApplyCardID"].value="请输入...";
        document.getElementById("ApplyCardID").disabled=true;
        document.getElementById("ApplyCardID").style.background="Gainsboro";
    }
    else
    {
        document.form1.elements["ApplyCardID"].value="由系统自动分配...";
        document.getElementById("ApplyCardID").disabled=false;
        document.getElementById("ApplyCardID").style.background="#ffffff";
    }
}
</script>
</form>