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Please see the official X‑Plane Support page for help.
If nVidia card there’s two main settings that in default configuration will slow down XP. Launch nVidia control panel (Windows, right click on desktop, you'll see the option). Select Manage 3D settings, choose either Global Settings or per Program Settings and choose xPlane. Set Power Management Mode to PREFER MAX PERFORMANCE and set Threaded Optimization to OFF. That’ll help a bunch.
And, get nVidia driver 398.11 [as of early July 2018, a better one may come along so this isn't gospel], it seems to work really well with XP – faster, less artifacts and overall better quality.
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