private void txtArrears_KeyPress(object sender, KeyPressEventArgs e)
        {
            if (((e.KeyChar >= '0') && (e.KeyChar <= '9')) || (e.KeyChar == '.') || (e.KeyChar == (char)8) )
            {
                e.Handled = false;
            }
            else
            {
                e.Handled = true ;
            }
        }

private void txtArrears_KeyPress(object sender, KeyPressEventArgs e)
{
    if ((Control.ModifierKeys & Keys.Control) == Keys.Control) return;
    e.Handled = !(((e.KeyChar >= '0') && (e.KeyChar <= '9')) || 
        (e.KeyChar == '.') || (e.KeyChar == (char)8));
}

------解决方案--------------------
那个判断还可以简化为：
C# code
e.Handled = "0123456789.\x8".IndexOf(e.KeyChar) < 0;

------解决方案--------------------
onkeypress事件，写一小段JS代码即可

------解决方案--------------------
友情提示：鼠标的动作也要考虑，比如右键的粘帖，直接拖过来的数据等等~~~~~