正在加载页面loading的制作

js:
function checkbutton()
        {
            if(document.all.txtBackupAddr.value == "" && document.all.ddlBackup.options[document.all.ddlBackup.selectedIndex].value == "备份")
            {
            alert("请输入地址。");
            document.all.txtBackupAddr.focus();
            }
            else
            {
            document.all.lbBusy.style.left=eval((document.body.offsetWidth-document.all.lbBusy.style.width.replace("px",""))/2);
            document.all.lbBusy.style.top=eval(document.body.offsetHeight-document.all.lbBusy.style.height.replace("px",""))-100;
            document.all.lbBusy.style.display="";
            document.all.btSave2.disabled=true;
            __doPostBack('btSave','');
            //document.Form1.submit();
            }
        }


</TR>                        </TABLE>
                        <DIV id="lbBusy" style="BORDER-RIGHT: 1px dashed; BORDER-TOP: 1px dashed; DISPLAY: none; BORDER-LEFT: 1px dashed; WIDTH: 280px; BORDER-BOTTOM: 1px dashed; POSITION: absolute; HEIGHT: 85px; BACKGROUND-COLOR: #f7f1e3"
                            ms_positioning="FlowLayout"><FONT face="宋体"></FONT><BR>
                            <BR>
                            系统正在保存信息，请稍候</DIV>

.
<INPUT class="presslong" id="btSave2" onclick="checkbutton();" type="button" value="保存信息">
                        <asp:button id="btSave" runat="server" CssClass="presslong" Visible="False" Text="保存信息"></asp:button>