How to use Ajax for FileUpload?

[thupham]

I use Visual Studio 2003, and Ajax.dll
In design, I have :
1 FileField, named: FileInput, set runnat="server"
1 Button (of Html toolbox), named: cmdUpload
1 Label (of HTML toolbox), named: lblInfo
First I create function for customer upload their file to server on click event:

private void cmdUpload_Click(object sender, System.EventArgs e)
        {
            if (FileInput.PostedFile.FileName == "") 
            {
                lblInfo.Text = "No file specified.";
            } 
            else 
            {
                try 
                {
                    if (FileInput.PostedFile.ContentLength > 1048576) 
                    {
                        lblInfo.Text = "File is too large.";
                    }
                    else 
                    {
                        string fileName = Path.GetFileName(FileInput.PostedFile.FileName);
                        string filepath = Server.MapPath("") +"\\bin\\CustomerPic\\"+fileName;
                        FileInput.PostedFile.SaveAs(filepath);
                        lblInfo.Text = "File " + fileName + " uploaded.";
                    }
                }
                catch (Exception err) 
                {
                    lblInfo.Text = err.Message;
                }
            }
        }

This function is successful, then I want to use Ajax when Customer click on cmdUpload, I don't set FileInput runnat="server", so code behind can't see FileInput.
Can you give value of FileInput.PostFile in code behind.
Or you can tell me other way to use ajax for FileUpload.
I hope to have true answer than other.
Thanks.