Centering Modal Popup Extender? (Edited)

Hello again,
I have a problem: i cant get a modal popup control to be centered!
The problem occures in some resolutions...
The control isn't in any divs or something like that, but i tried to put it in center aligned divs, no effect...
Edit:see last reply.

At 1280*1024 resolution, no problem:

(Link:http://www.intensitysoft.info/txtFiles/1280,1024.JPG)

At 14490,900 resolution, no problem:

(Link:http://www.intensitysoft.info/txtFiles/14490,900.JPG)

At 1280*800 resolution... BIG problem :):

(Link:http://www.intensitysoft.info/txtFiles/1280,800.JPG)

As you can see the panel is totally left...

Thanks for any help,
Liran.

The page seems to work fine in all my resolutions, but I don;t have 1280 X 800 available on any of my box's. Could you please post your code, maybe something will jump out.

-Alan

<%@. Page Language="C#" MasterPageFile="~/MasterPage.master" AutoEventWireup="true" CodeFile="products.aspx.cs" Inherits="Default4"%>
<asp:Content ID="Content1" ContentPlaceHolderID="ContentPlaceHolder1" Runat="Server">
<asp:Repeater ID="Repeater1" runat="server" DataSourceID="AccessDataSource1">
<SeparatorTemplate>
<br />
</SeparatorTemplate>
<ItemTemplate>
<table cellpadding="0" cellspacing="0" style="width: 100%; height: 10px; border-top-width: 1px; border-left-width: 1px; border-left-color: #33cccc; border-bottom-width: 1px; border-bottom-color: #33cccc; border-top-color: #33cccc; border-right-width: 1px; border-right-color: #33cccc;">
<tr>
<td style="font-weight: bold; font-size: 16px; text-transform: none; color: black; font-family: Arial; background-color: #3399cc; text-decoration: none;" colspan="2">
<%# Eval("siteName") %></td>
</tr>
<tr style="background-color: lightblue; font-size: 14px; color: black; font-family: Arial;">
<td style="width: 133px; height: 90%">
<asp:ImageButton ImageUrl='<%# Eval("thumbPicSrc") %>' ID="ImageButton1" runat="server" />
</td>
<td style="height: 90%" valign="top">
<%# Eval("description") %></td>
</tr>
</table>

<ajaxToolkit:ModalPopupExtender OkControlID="imgOk" BackgroundCssClass="modalBackground" ID="ModalPopupExtender1" TargetControlID="ImageButton1" runat="server" PopupControlID="Panel1" />
<asp:Panel ID="Panel1" runat="server" style="display: none">
<asp:ImageButton ImageUrl='<%# Eval("picSrc") %>' ID="imgOk" runat="server" />
<br />
</asp:Panel>

</ItemTemplate>
</asp:Repeater>
<asp:AccessDataSource ID="AccessDataSource1" runat="server" DataFile="App_Data\instensUsersDB.mdb"
SelectCommand="SELECT * FROM [sites]"></asp:AccessDataSource>
<asp:ScriptManager id="ScriptManager1" runat="server" />

<br />

<br />
</asp:Content>

Just found out that the problem doesn't occur because of the resolution, it occures because of the browser!
With Internet Explorer 7 everything is fine, so on with FireFox... but with I.E. 6, it's just doesnt work.

Any solution?
Liran.