Powershell script - adds custom site column to content type (MOSS)

Used this script today to add a custom site column (Forarchive) to the core Content Type - Document

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[void][System.Reflection.Assembly]::Load("Microsoft.Office.Server.Search, Version=12.0.0.0, Culture=neutral, PublicKeyToken=71e9bce111e9429c")

[void][System.Reflection.Assembly]::Load("Microsoft.Sharepoint, Version=12.0.0.0, Culture=neutral, PublicKeyToken=71e9bce111e9429c")

[void][System.Reflection.Assembly]::Load("Microsoft.Office.Server, Version=12.0.0.0, Culture=neutral, PublicKeyToken=71e9bce111e9429c")

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$url = "http:///sites/sitename/"

$site = new-object Microsoft.SharePoint.SPSite($URL)

$web = $site.RootWeb

$ct=$web.ContentTypes["Document"];

$fieldAdd=$web.Fields["ForArchive"]

$fieldLink=New-Object Microsoft.SharePoint.SPFieldLink($fieldAdd)

$ct.FieldLinks.Add($fieldLink);

$ct.Update()

$web.Dispose()

$site.Dispose()