[Alyona]

<div id="inputsize">
                    <input type="hidden" id="inputsizecount" name="inputsizecount" value="3">
                    <table width="450px">
                        <tr height="28px"><td>Длина</td><td><input name="length0" id="myid" value="10.2" size="10"></td>
                            <td colspan="2" rowspan="1"><input type="checkbox"  
                                checked="checked"                         onclick="if(this.checked){document.getElementById('discount0').style.display='inline-block'; document.getElementById('price0').style.display='none';}else {document.getElementById('price0').style.display='inline-block'; document.getElementById('discount0').style.display='none';}">
                            Цена со скидкой</td>
                        </tr>
                        <tr><td>Ширина</td><td><input name="width0" id="myid" value="10.1" size="10"></td>
                            <td colspan="2" rowspan="2" width="150px" height="55px">
                                <p id="discount0" style="display:inline-block">Старая цена<input name="oldprice0" id="myid" value="1000" size="10"><br />
                                    Новая цена<input name="newprice0" id="myid" value="500" size="10">
                                </p>
                                <p id="price0" style="display:none">Цена<input name="price0" id="myid" value="500" size="10">
                                </p>
                            </td>
                        </tr>
                        <tr><td>Высота</td><td><input name="height0" id="myid" value="10" size="10"></td>
                        </tr>
                    </table>
                    <br />
                <div>
                            <table width="450px">
                                <tr height="28px"><td>Длина</td><td><input name="length1" id="myid" value="10" size="10"></td>
                                    <td colspan="2" rowspan="1"><input type="checkbox" checked="checked" onclick="if(this.checked){document.getElementById('discount1').style.display='inline-block'; document.getElementById('price1').style.display='none';}else {document.getElementById('price1').style.display='inline-block'; document.getElementById('discount1').style.display='none';}">
                                    Цена со скидкой</td>
                                </tr>
                                <tr><td>Ширина</td><td><input name="width1" id="myid" value="10" size="10"></td>
                                    <td colspan="2" rowspan="2" width="150px" height="55px">
                                        <p id="discount1" style="display:inline-block">Старая цена<input name="oldprice1" id="myid" value="1200.2" size="10"><br />
                                            Новая цена<input name="newprice1" id="myid" value="1000" size="10">
                                        </p>
                                        <p id="price1" style="display: 
                                        none                                            ">Цена&nbsp;<input name="price1" id="myid" value="1000" size="10">
                                        </p>
                                    </td>
                                </tr>
                                <tr><td>Высота</td><td><input name="height1" id="myid" value="15" size="10"></td>
                                </tr>
                            </table>
                            <br />
                        </div>
                   <div>
                            <table width="450px">
                                <tr height="28px"><td>Длина</td><td><input name="length2" id="myid" value="12" size="10"></td>
                                    <td colspan="2" rowspan="1"><input type="checkbox" checked="checked" onclick="if(this.checked){document.getElementById('discount2').style.display='inline-block'; document.getElementById('price2').style.display='none';}else {document.getElementById('price2').style.display='inline-block'; document.getElementById('discount2').style.display='none';}">
                                    Цена со скидкой</td>
                                </tr>
                                <tr><td>Ширина</td><td><input name="width2" id="myid" value="10" size="10"></td>
                                    <td colspan="2" rowspan="2" width="150px" height="55px">
                                        <p id="discount2" style="display:inline-block">Старая цена&nbsp;<input name="oldprice2" id="myid" value="12.5" size="10"><br />
                                            Новая цена<input name="newprice2" id="myid" value="10" size="10">
                                        </p>
                                        <p id="price2" style="display: 
                                        none                                            ">Цена<input name="price2" id="myid" value="10" size="10">
                                        </p>
                                    </td>
                                </tr>
                                <tr><td>Высота</td><td><input name="height2" id="myid" value="11.1" size="10"></td>
                                </tr>
                            </table>
                            <br />
                        </div>
                   <div>
                            <table width="450px">
                                <tr height="28px"><td>Длина</td><td><input name="length3" id="myid" value="10" size="10"></td>
                                    <td colspan="2" rowspan="1"><input type="checkbox" onclick="if(this.checked){document.getElementById('discount3').style.display='inline-block'; document.getElementById('price3').style.display='none';}else {document.getElementById('price3').style.display='inline-block'; document.getElementById('discount3').style.display='none';}">
                                    Цена со скидкой</td>
                                </tr>
                                <tr><td>Ширина</td><td><input name="width3" id="myid" value="10" size="10"></td>
                                    <td colspan="2" rowspan="2" width="150px" height="55px">
                            <p id="discount3" style="display:none">Старая цена<input name="oldprice3" id="myid" value="0" size="10"><br />
                                            Новая цена<input name="newprice3" id="myid" value="500" size="10">
                                        </p>
                                        <p id="price3" style="display: 
                                        inline-block                                            ">Цена&nbsp;<input name="price3" id="myid" value="500" size="10">
                                        </p>
                                    </td>
                                </tr>
                                <tr><td>Высота</td><td><input name="height3" id="myid" value="11" size="10"></td>
                                </tr>
                            </table>
                            <br />
                        </div>
</div>
<input type="button" onclick="add_inputsize()" value="Добавить размер">
<input type="button" onclick="del_inputsize()" value="Убрать последний">