Screw both of these options, you HAVE to try out this app. As long as the domain controller (or other machine on a local subnet, for that matter) has network access to the machine you want to support, you HAVE to try out Dameware Mini Remote Control. Full domain authenticated desktop access in seconds, no stupid scrolly windows if there are screen resolution discrepancies or weird line-scan-refresh issues with VNC, and you can connect to non-domain computers if you have the credentials.
http://www.dameware.com/products/dmrc/
And uh, it's $89. Would be better if it was free, but damn it works good for the money.
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