Remote controlling (shadow) XP's user session

On the target WinXp box:
enable file-and-print sharing at the firewall
enable Remote-Desktop at the firewall
reg add "HKLM\System\CurrentControlSet\Control\Termina l Server" /v
AllowRemoteRPC /t REG_DWORD /d 0x1 /f
[Optional:
Change the policy `Set Rules for remote control of terminal services user
sessions` to `Full Control` / `View`]
reboot
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Source:
Shadow Console on XP Pro SP2
www.mombu.com/microsoft/windows-terminal-services/
t-shadow-console-on-xp-pro-sp2-994408.html

Additional info:
If you want to be able to browse to the XP client instead of using the "Actions" - "Connect to Computer..." menu in TS Manager, then you'll also have to change the value of this registry entry on the XP client:

HKEY_LOCAL_MACHINE\System\CurrentControlSet\Control\Terminal Server
"TSAdvertise" = REG_DWORD:1
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Source:
How can I Remote Control my Windows XP SP2 client from within Terminal Services Manager?
http://ts.veranoest.net/ts_faq_administration.htm#XPSP2remote