installation problem on 64 bit OS

I am getting an installation problem for sample WIA scanner driver
(present in ddk sample) on 64 bit OS. I have two OS builds of XP 3790
and 3787. I could able to install the driver on 3787 and could able to
initiate the scan but on 3790 build I could able to install the driver,
but above the WIA driver KSTHUNK.SYS upper filter driver in getting
attached, due to which the scan is failing.
I want to clarify some of the issues

  1. In which circumstances does thunk drivers are installed ? And who
    will takes care of installing the thunk drivers ?
  2. Is it possible to avoid installing these thunk drivers from our inf
    file? Or is there any other method to avoid automatic
    installation of thunk drivers ?
  3. Since the problem is arising on 3790 but not on 3787 build, does it
    points out that the problem is with versions of the builds ?
  4. The WIA scanner driver is a user mode driver which runs as a COM
    service, is this is the issue due to which thunk driver is
    installing ?