my code:
<CuteWebUI:Uploader runat="server" ID="Uploader1" InsertButtonID="Button1" OnFileUploaded="Uploader1_FileUploaded" MultipleFilesUpload="true">
<VALIDATEOPTION AllowedFileExtensions="jpeg, jpg, gif, png, zip, doc, rtf, pdf" MaxSizeKB="102400" />
</CuteWebUI:Uploader>
<asp:Button ID="Button1" runat="server" Text="CustomButton"/>
And I use fancybox to show this page inside an iframe modal.