File seek in Javascript (FileSystemObject)

Question

Hello,

I am trying to open a binary file and add some data in a specific position (after byte 29). This is my code:

function exportFile(text)
{
    var fso, f2;
    fso = new ActiveXObject("Scripting.FileSystemObject");
    f2 = fso.OpenTextFile("C:\\Users\\Devesa\\Documents\\"+url,8);
    f2.Skip(29);
    f2.Write(text);
    f2.Close;
}

But I get this problems:

1. Data is added only at the end of the file, I cannot seek the byte 29 before writing.
2. I'm afraid that opening the file with "OpenTextFile" I won't be able to write any byte (only text). Right?
3. On Internet Explorer I always get some "security advices" and it doesn't work in any other browser.

THANKS