you have to run it in compatibility mode. right click>file properties>compatibility?? something like that anyway. You can then select the windows OS version emulation to run OllyDbg in.
I've heard bad things about trying to run Olly on 64bit Vista. I've stuck with WinDbg for those cases. However, I have had reasonable success on 32bit Vista - though, this was without using any plugins at all. And some functionality didn't work too well. It helps to set it up to automatically run as admin (though this is only really necessary if you want to attach to another process).
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