You should be able to run Opus as Administrator on XP, it's just a question of making sure you do it properly:
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Full exit Opus. Don't just close the windows, but exit it. See this FAQ for details.
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Find dopus.exe using Explorer, hold shift and right-click it. Then use the Run As menu as usual.
That should start dopus.exe as Administrator.
(FWIW, on Vista this kind of stuff is built-in using UAC and you can run individual commands, or toggle individual lister windows, as administrator.)