Vista - Controlling Internet Explorer

I am writing a powershell script to attempt to assist our call centre agents
with data capture. They must fill in two websites with almost identical
questions (but different order and on different pages of the application).
Follow part of Powershell in Action I am attempting to control Internet
Explorer. I can then grab the values from one DOM and copy them into the DOM
of the other window. In addition to this I have a Windows form set to always
on top which allows the agent to control the copying and also which window is
displayed. This is as we run their IE in full screen kiosk mode.

So there is something like this (Variable names changed to remove company
names):

$ie1 = New-Object -com "InternetExplorer.Application"
$ie1.Visible = $true
$ie1.FullScreen = $true
$ie1.Navigate2($url1)

Same for $ie2

$form = New-Object Windows.Forms.Form
$buttonDisplay1 = New-Object Windows.Forms.Button
$buttonDisplay1.Text = "Display 1"
$buttonDisplay1.Dock = "fill"
$buttonDisplay1.add_click({
$ie1.Visible = $true
$ie2l.Visible = $false
})
.......
.......
$form.ShowDialog()

This all works fine when I use navigate2 to change to a file on my local
machine (e.g. C:\example.html). I can then press the copy button, press the
switch window button.

However as soon as I change the parameter to any HTTP address then it stops
working. The window DOES navigate to the URL but then the COM object becomes
disconnected showing the following error:
Exception setting "Visible": "The object invoked has disconnected from its
clients. (Exception from HRESULT: 0x80010108
(RPC_E_DISCONNECTED))"

Does anyone know why this may be? My initial thoughts are that it is some
sort of security policy, but then why does it navigate before disconnnecting?

Thanks,
Martin.

I've found that actually whenever I call navigate2 it actually opens another
IE window in which to load the URL. But it reuses this new window for each
subsequent navigate but opens a new tab. This is quite problematic when
trying to change pages within the same application form.