Example Async WinForm

Add-Type -AssemblyName System.Windows.Forms

# Defining a synchronized hashtable allows us to add and retrieve objects in a 'thread-safe' manner.
$ht = [hashtable]::Synchronized(@{})

# Creates a runspace that is attached to a newly-created PowerShell instance.
Function New-Runspace()
{
    $rs = [runspacefactory]::CreateRunspace()
    $rs.ApartmentState = "STA"
    $rs.ThreadOptions = "ReuseThread"
    $rs.Open()
    $rs
}

# New-PowerShell creates a PowerShell instance within the specified runspace and runs the supplied ScriptBlock.
Function New-PowerShell([scriptblock] $ScriptBlock, [runspace] $Runspace)
{
    $ps = [powershell]::Create().AddScript($ScriptBlock)
    $ps.Runspace = $Runspace
    $ps.BeginInvoke()
}

# The main form that is displayed.
$form = New-Object System.Windows.Forms.Form -Property @{
    Height = 150
    Width = 600
}

# This TextBox is where your 'systeminfo.exe' results will go.
# As soon as the systeminfo text is added, this TextBox and the
# Form will resize themselves to fit the content.
$statusBox = New-Object System.Windows.Forms.TextBox -Property @{
    Height = 30
    Width = 580
    Location = "10, 50"
    MultiLine = $true
    ScrollBars = [System.Windows.Forms.ScrollBars]::Both
    WordWrap = $false
    Add_TextChanged = {

        $count = $statusBox.Lines.Length
        $possibleHeight = $count * $statusBox.Font.Height
        if ($possibleHeight -gt 800)
        {
            $possibleHeight = 800
        }
        $statusBox.Height = $possibleHeight
        $form.Height = $possibleHeight + 100

    }
}
$ht.Add("StatusBox", $statusBox)    # Add $statusBox to the 'synchronized' hashtable so it can be called safely
                                    # from within a runspace.

# This is the button that starts the 'systeminfo.exe' process.
# Notice, because it will run the 'systeminfo.exe' process in a separate thread,
# the GUI remains responsive.  You can even click the "DummyButton" all day long while
# the operation is running.
$button = New-Object System.Windows.Forms.Button -Property @{
    Text = "Get System Info"
    Width = 150
    Location = "20, 10"
    Name = "MyButton"
    # This is the Click Event handler that calls 'systeminfo.exe' asynchronously.
    Add_Click = {
        $rs = New-Runspace
        $rs.SessionStateProxy.SetVariable("ht", $ht)    # We add the synchronized hashtable to the InitialSessionState.
                                                        # This allows us to reference $ht from within the runspace.

        # $code represents the scriptblock that calls 'systeminfo.exe'
        $code = {
            $message = systeminfo.exe       # Run the systeminfo.exe like normal.
                                            # We do NOT pipe it to 'Out-String' as we want
                                            # to be able to retain and query the line count.

            $ht.StatusBox.Lines = $message  # Add the entire message to the StatusBox's Lines property.
                                            # We are referencing it from the synchronized hashtable.
        }
        New-PowerShell -ScriptBlock $code -Runspace $rs
    }
}

# This is just a dummy button object that you can click to show
# that the GUI remains responsive while 'systeminfo.exe' is running
# in the background.
$dummyButton = New-Object System.Windows.Forms.Button -Property @{
    Text = "Dummy Button"
    Width = 100
    Location = "180, 10"
    Name = "DummyButton"
}

$form.Controls.AddRange(@($button, $dummyButton, $statusBox))
$form.ShowDialog()