Ok, I'm a goober.
I just figured out how to run multiple SDI interfaces of Opera, so I can have one set of windows for work stuff, and one set of windows for non-work stuff, and have both setups saved and whatnot. This pleases me immensely. I am such a goober. :)
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accomplished
Set up all your windows the way you want them, and then go to File -> Sessions -> Save session. Name it "work" or "not work" or whatever you want. Then, do the same for the other instance you want, obviously naming it something else. Then, when you go to File -> Sessions -> Open Session and open the currently not open one (that made sense, really), it pops up an entirely new instance of Opera with the selected session. Like I said, this is under Windows, but I'll keep my fingers crossed for you. Also, in case it matters, this is running Opera 7.
Good luck!