We use a product called securecopy from Script logic
http://www.scriptlogic.com/Products/securecopy/
Really great tool for file server migrations...not free
For a free tool you may want to give Microsofts' rich copy a try
http://technet.microsoft.com/en-us/magazine/2009.04.utilityspotlight.aspx?pr=blog
Full disclousre: I haven't tested RichCopy yet.
Thanks
Mike