HTML: Is it possible to have a FORM tag in each TABLE ROW in a XHTML valid way?

You can't. Your only option is to divide this into multiple tables and put the form tag outside of it. You could end up nesting your tables, but this is not recommended:

<table>
  <tr><td><form>
    <table><tr><td>id</td><td>name</td>...</tr></table>
  </form></td></tr>
</table>

I would remove the tables entirely and replace it with styled html elements like divs and spans.

The answer of @wmantly is basicly 'the same' as I would go for at this moment. Don't use <form> tags at all and prevent 'inappropiate' tag nesting. Use javascript (in this case jQuery) to do the posting of the data, mostly you will do it with javascript, because only one row had to be updated and feedback must be given without refreshing the whole page (if refreshing the whole page, it's no use to go through all these trobules to only post a single row).

I attach a click handler to a 'update' anchor at each row, that will trigger the collection and 'submit' of the fields on the same row. With an optional data-action attribute on the anchor tag the target url of the POST can be specified.

Example html

<table>
    <tbody>
        <tr>
            <td><input type="hidden" name="id" value="row1"/><input name="textfield" type="text" value="input1" /></td>
            <td><select name="selectfield">
                <option selected value="select1-option1">select1-option1</option>
                <option value="select1-option2">select1-option2</option>
                <option value="select1-option3">select1-option3</option>
            </select></td>
            <td><a class="submit" href="#" data-action="/exampleurl">Update</a></td>
        </tr>
        <tr>
            <td><input type="hidden" name="id" value="row2"/><input name="textfield" type="text" value="input2" /></td>
            <td><select name="selectfield">
                <option selected value="select2-option1">select2-option1</option>
                <option value="select2-option2">select2-option2</option>
                <option value="select2-option3">select2-option3</option>
            </select></td>
            <td><a class="submit" href="#" data-action="/different-url">Update</a></td>
        </tr>
        <tr>
            <td><input type="hidden" name="id" value="row3"/><input name="textfield" type="text" value="input3" /></td>
            <td><select name="selectfield">
                <option selected value="select3-option1">select3-option1</option>
                <option value="select3-option2">select3-option2</option>
                <option value="select3-option3">select3-option3</option>
            </select></td>
            <td><a class="submit" href="#">Update</a></td>
        </tr>
    </tbody>
</table>

Example script

    $(document).ready(function(){
        $(".submit").on("click", function(event){
            event.preventDefault();
            var url = ($(this).data("action") === "undefined" ? "/" : $(this).data("action"));
            var row = $(this).parents("tr").first();
            var data = row.find("input, select, radio").serialize();
            $.post(url, data, function(result){ console.log(result); });
        });
    });

A JSFIddle

You just have to put the <form ... > tag before the <table> tag and the </form> at the end.

Hopte it helps.

<table > 
<thead > 
   <tr>
    <th>No</th><th>ID</th><th>Name</th><th>Ip</th><th>Save</th> 
   </tr>
</thead>
<tbody id="table_data"> 
         <tr>
            <td> 
                <form method="POST" autocomplete="off" id="myForm_207" action="save.php">
                    <input type="hidden" name="pvm" value="207"> 
                    <input type="hidden" name="customer_records_id" value="2"> 
                    <input type="hidden" name="name_207" id="name_207" value="BURÇİN MERYEM ONUK"> 
                    <input type="hidden" name="ip_207" id="ip_207" value="89.19.24.118"> 

                </form> 
                1 
            </td> 
            <td> 
                207 
            </td> 
            <td> 
                <input type="text" id="nameg_207" value="BURÇİN MERYEM ONUK"> 
            </td> 
            <td> 
                <input type="text" id="ipg_207" value="89.19.24.118"> 
            </td> 
            <td>
                <button type="button" name="Kaydet_207" class="searchButton" onclick="postData('myForm_207','207')">SAVE</button>
            </td>
        </tr> 
        <tr>
            <td> 
                <form method="POST" autocomplete="off" id="myForm_209" action="save.php">
                    <input type="hidden" name="pvm" value="209"> 
                    <input type="hidden" name="customer_records_id" value="2"> 
                    <input type="hidden" name="name_209" id="name_209" value="BALA BAŞAK KAN"> 
                    <input type="hidden" name="ip_209" id="ip_209" value="217.17.159.22"> 
                </form> 
                2 
            </td> 
            <td> 
                209 
            </td> 
            <td> 
                <input type="text" id="nameg_209" value="BALA BAŞAK KAN"> 
            </td> 
            <td> 
                <input type="text" id="ipg_209" value="217.17.159.22"> 
            </td> 
            <td>
                <button type="button" name="Kaydet_209" class="searchButton" onclick="postData('myForm_209','209')">SAVE</button>
            </td>
        </tr> 
</tbody> 
</table> 
<script> 
function postData(formId,keyy){ 
    //alert(document.getElementById(formId).length);
    //alert(document.getElementById('name_'+keyy).value);
    document.getElementById('name_'+keyy).value=document.getElementById('nameg_'+keyy).value;
    document.getElementById('ip_'+keyy).value=document.getElementById('ipg_'+keyy).value;

    //alert(document.getElementById('name_'+keyy).value);
    document.getElementById(formId).submit(); 
}
</script>