How do I show the output of a command called within a gui script

Question

I'm starting from scratch on a project I've been tasked with.  My intention is a quick down-and-dirty way to apply an image within winPE to apply a windows image to the machine I've booted to a usb drive loaded with winPE.
Here's my start.  It's rough, but, I have to start somewhere.
[void] [System.Reflection.Assembly]::LoadWithPartialName("System.Windows.Forms")
[void] [System.Reflection.Assembly]::LoadWithPartialName("System.Drawing")
$objForm = New-Object System.Windows.Forms.Form
$objForm.Text = "DISM"
$objForm.Size = New-Object System.Drawing.Size(600,400)
$objForm.AutoSizeMode = "GrowAndShrink"
$objForm.StartPosition = "CenterScreen"
$objForm.FormBorderStyle = "Fixed3D"
$objForm.KeyPreview = $True
Function do_DISM{
$dism = "dism /apply-image /imagefile:D:\W7x86.wim /index:1 /applydir:C:\"
Invoke-Expression $dism
$DISMButton = New-Object System.Windows.Forms.Button
$DISMButton.BackColor = "ButtonFace"
$DISMButton.Location = New-Object System.Drawing.Size(12,27)
$DISMButton.Size = New-Object System.Drawing.Size(120,25)
$DISMButton.TabIndex = 1
$DISMButton.Text = “Start DISM”
$DISMButton.Add_Click({do_DISM})
$objForm.Controls.Add($DISMButton)
$objForm.Add_Shown({$objForm.Activate()})
[void] $objForm.ShowDialog()
Now, this does work, and it will in fact apply the windows image to c:\ which is what I need it to do.  But, I have a few quesitons.
Am I correct to use "Invoke-Expression" in the function do_DISM to start the command?  According to technet's articles, yes, but, want to make sure I'm doing this the proper way, since I'm learning that calling Invoke-Expression isn't always
the way to do things.
Also, since this will be used by others in my group, I'm going to need to show some sort of progress report on how far along DISM is getting along, otherwise, 5 minutes into DISM running, some people are going to think nothing's happening, and just power
down the computer no matter what I tell them.  I know that running DISM from the command line, it will show a progress bar that is adequate for what I'm needing.  Running the script above and clicking the button, it does run, but, all in the background
with no progress indication.  Is there a way I can tell either in the function or when the function calls Invoke-Expression to run DISM, to open in a new command window which shows the live progress of the command running?
Again, my disclaimer: VERY new to writing bits of code, and am trying my best here, so, thanks in advance for patience with me.

Answer 1

That's exactly what I was looking for!  Thank you!
Changed code to:
$dism = "X:\Windows\System32\Cmd.exe /c start CMD /k dism /apply-image /imagefile:D:\W7x86.wim /index:1 /applydir:C:\"
And voila, new window opened with the live output of dism.
new... and have a glazed over look about my eyes to prove it...