MultiSelectListBox.ps1

# Original example posted at http://technet.microsoft.com/en-us/library/ff730950.aspx

Add-Type -AssemblyName System.Windows.Forms
Add-Type -AssemblyName System.Drawing

$form = New-Object System.Windows.Forms.Form 
$form.Text = "Data Entry Form"
$form.Size = New-Object System.Drawing.Size(300,200) 
$form.StartPosition = "CenterScreen"

$OKButton = New-Object System.Windows.Forms.Button
$OKButton.Location = New-Object System.Drawing.Point(75,120)
$OKButton.Size = New-Object System.Drawing.Size(75,23)
$OKButton.Text = "OK"
$OKButton.DialogResult = [System.Windows.Forms.DialogResult]::OK
$form.AcceptButton = $OKButton
$form.Controls.Add($OKButton)

$CancelButton = New-Object System.Windows.Forms.Button
$CancelButton.Location = New-Object System.Drawing.Point(150,120)
$CancelButton.Size = New-Object System.Drawing.Size(75,23)
$CancelButton.Text = "Cancel"
$CancelButton.DialogResult = [System.Windows.Forms.DialogResult]::Cancel
$form.CancelButton = $CancelButton
$form.Controls.Add($CancelButton)

$label = New-Object System.Windows.Forms.Label
$label.Location = New-Object System.Drawing.Point(10,20) 
$label.Size = New-Object System.Drawing.Size(280,20) 
$label.Text = "Please make a selection from the list below:"
$form.Controls.Add($label) 

$listBox = New-Object System.Windows.Forms.Listbox 
$listBox.Location = New-Object System.Drawing.Point(10,40) 
$listBox.Size = New-Object System.Drawing.Size(260,20) 

$listBox.SelectionMode = "MultiExtended"

[void] $listBox.Items.Add("Item 1")
[void] $listBox.Items.Add("Item 2")
[void] $listBox.Items.Add("Item 3")
[void] $listBox.Items.Add("Item 4")
[void] $listBox.Items.Add("Item 5")

$listBox.Height = 70
$form.Controls.Add($listBox) 
$form.Topmost = $True

$result = $form.ShowDialog()

if ($result -eq [System.Windows.Forms.DialogResult]::OK)
{
    $x = $listBox.SelectedItems
    $x
}