How to enlarge an image to work in all the browsers

Hi,
I am using a repeater to show images. The thing is that every image has different size that is the reason why I am using a div to put all  the images with the same size but I would like to enlarge the image when the event onmouseover. I have read a lot about this but I have not found anything that works with all the browsers. This is my code

 <asp:repeater id="DatagridCartoons" runat="server">
        <ItemTemplate>
            <div style="margin-left: 20px; float: left; margin-bottom: 10px; width: 170px; height:100px; overflow:hidden; min-height:80px;">
                 <a href='<%# Access.return_link_cartoon(DataBinder.Eval(Container.DataItem,"id")) %>'><asp:Image
 ToolTip='< ...