<asp:GridView ID="grdtemp" runat=”server” CssClass="mytable" AutoGenerateColumns="true" onmouseup="TableResize_OnMouseUp(this);"
onmousedown="TableResize_OnMouseDown(this);">

var oResizeTarget = null;
var iStartX = null;
var iEndX = null;
var iSizeX = null;
var sResizableElement = "TH";   
var iResizeThreshold = 8;
var iEdgeThreshold = 8;
var iSizeThreshold = 20;
var sVBarID = "VBar";

function TableResize_CreateVBar()
{
    // Returns a reference to the resizer VBar for the table
    var objItem = document.getElementById(sVBarID);

    // Check if the item doesn't yet exist
    if (!objItem) 
    {        
        // and Create the item if necessary
        objItem = document.createElement("SPAN");

        // Setup the bar
        objItem.id = sVBarID;
        objItem.style.position = "absolute";
        objItem.style.top = "0px";
        objItem.style.left = "0px";
        objItem.style.height = "0px";
        objItem.style.width = "2px";
        objItem.style.background = "silver";
        objItem.style.borderLeft = "1px solid black";
        objItem.style.display = "none"; 

        // Add the bar to the document
        document.body.appendChild(objItem);
    }
}

window.attachEvent("onload", TableResize_CreateVBar);

function TableResize_GetOwnerHeader(objReference) 
{
    var oElement = objReference;

    while (oElement != null && oElement.tagName != null && oElement.tagName != "BODY") 
    {
        if (oElement.tagName.toUpperCase() == sResizableElement) 
        {
            return oElement;
        }

        oElement = oElement.parentElement;
    }

    // The TH wasn't found
    return null;
}

function TableResize_GetFirstColumnCell(objTable, iCellIndex) 
{
    var oHeaderCell = objTable.rows(0).cells(iCellIndex);

    return oHeaderCell;
}
function TableResize_CleanUp() 
{
    // Void the Global variables and hide the resizer VBar.
    var oVBar = document.getElementById(sVBarID);

    if (oVBar)
    {
        oVBar.runtimeStyle.display = "none";
    }

    iEndX = null;
    iSizeX = null;
    iStartX = null;
    oResizeTarget = null;
    oAdjacentCell = null;

    return true;
}
function TableResize_OnMouseMove(objTable) 
{
    // Change cursor and store cursor position for resize indicator on column
    var objTH = TableResize_GetOwnerHeader(event.srcElement);

    if (!objTH)
        return;

    var oVBar = document.getElementById(sVBarID);

    if (!oVBar)
        return;

    var oAdjacentCell = objTH.nextSibling;

    // Show the resize cursor if we are within the edge threshold.
    if ((event.offsetX >= (objTH.offsetWidth - iEdgeThreshold)) && (oAdjacentCell != null)) 
    {
        objTH.runtimeStyle.cursor = "e-resize";
    } 
    else 
    {
        if(objTH.style.cursor) 
        {
            objTH.runtimeStyle.cursor = objTH.style.cursor;
        } 
        else 
        {
            objTH.runtimeStyle.cursor = "";
        }
    }
if (oVBar.runtimeStyle.display == "inline") 
    {
        // We have to add the body.scrollLeft in case the table is wider than the view window
        // where the table is entirely within the screen this value should be zero...
        oVBar.runtimeStyle.left = window.event.clientX + document.body.scrollLeft;

        document.selection.empty();
    }

    return true;
}
function TableResize_OnMouseDown(objTable) 
{
    // Record start point and show vertical bar resize indicator
    var oTargetCell = event.srcElement;

    if (!oTargetCell)
        return;

    var oVBar = document.getElementById(sVBarID);

    if (!oVBar)
        return;

    if (oTargetCell.parentElement.tagName.toUpperCase() == sResizableElement)
    {
        oTargetCell = oTargetCell.parentElement;
    }

    var oHeaderCell = TableResize_GetFirstColumnCell(objTable, oTargetCell.cellIndex);

    if ((oHeaderCell.tagName.toUpperCase() == sResizableElement) && (oTargetCell.runtimeStyle.cursor == "e-resize")) 
    {        
        iStartX = event.screenX;
        oResizeTarget = oHeaderCell;

        // Mark the table with the resize attribute and show the resizer VBar.
        // We also capture all events on the table we are resizing because Internet 
        // Explorer sometimes forgets to bubble some events up. 
        // Now all events will be fired on the table we are resizing.
        objTable.setAttribute("Resizing", "true");
        objTable.setCapture();

        // Set up the VBar for display

        // We have to add the body.scrollLeft in case the table is wider than the view window
        // where the table is entriely within the screen this value should be zero...
        oVBar.runtimeStyle.left = window.event.clientX + document.body.scrollLeft;

        oVBar.runtimeStyle.top = objTable.parentElement.offsetTop + objTable.offsetTop;;
        oVBar.runtimeStyle.height = objTable.parentElement.clientHeight;
        oVBar.runtimeStyle.display = "inline";
    }

    return true;
}

function TableResize_OnMouseUp(objTable) 
{
    // Resize the column and its adjacent sibling if position and size are within threshold values
    var oAdjacentCell = null;
    var iAdjCellOldWidth = 0;
    var iResizeOldWidth = 0;

    if (iStartX != null && oResizeTarget != null) 
    {
        iEndX = event.screenX;
        iSizeX = iEndX - iStartX;

        // Mark the table with the resize attribute for not resizing
        objTable.setAttribute("Resizing", "false");

        if ((oResizeTarget.offsetWidth + iSizeX) >= iSizeThreshold) 
        {
            if (Math.abs(iSizeX) >= iResizeThreshold) 
            {
                if (oResizeTarget.nextSibling != null) 
                {
                    oAdjacentCell = oResizeTarget.nextSibling;
                    iAdjCellOldWidth = (oAdjacentCell.offsetWidth);
                } 
                else 
                {
                    oAdjacentCell = null;
                }

                iResizeOldWidth = (oResizeTarget.offsetWidth);
                oResizeTarget.style.width = iResizeOldWidth + iSizeX;

                if ((oAdjacentCell != null) && (oAdjacentCell.tagName.toUpperCase() == sResizableElement)) 
                {
                    oAdjacentCell.style.width = (((iAdjCellOldWidth - iSizeX) >= iSizeThreshold)?(iAdjCellOldWidth - iSizeX):(oAdjacentCell.style.width = iSizeThreshold))
                }
            }
        } 
        else 
        {
            oResizeTarget.style.width = iSizeThreshold;
        }
    }

    // Clean up the VBar and release event capture.
    TableResize_CleanUp();
    objTable.releaseCapture();

    return true;
}

css content:

.tablecontainer
{
    position: absolute;
}

.mytable
{
    table-layout: fixed;    
}

.mytable TD, .mytable TH
{
    border: solid 1px black;
    width: 120px;
}

.mytable TH
{
    background-color: #e0e0e0;    
}