Hemesh,

Unfortunately, the Click event that is triggered doesn't really let you know which mouse button that was pressed, only that the control was clicked.  Fortunately, since a Click event is really just a MouseDown followed by a MouseUp, you could keep track of this yourself in the MouseUp on whether to ignore the Click or not:

private MouseButtons lastMouseButtons;
private void ultraGrid1_ClickCellButton(object sender, Infragistics.Win.UltraWinGrid.CellEventArgs e)
{
    if (this.lastMouseButtons == MouseButtons.Left)
    {
        // Process the click
        string s = "BL";
    }
}

private void ultraGrid1_MouseUp(object sender, MouseEventArgs e)
{
    this.lastMouseButtons = e.Button;
}

You should also take a look at this KB article in case you want to determine which UIElement the user has clicked on:

HOWTO:Taking action when right-clicking the WinGrid

Sometimes simply checking the grid.DisplayLayout.UIElement.LastElementEntered is enough as well.

-Matt