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Based on my experience, XOOPS and other PHP applications run much better on Linux. That being said, I do have a few sites that operate successfully on Windows, but not as well as my sites on Linux.
On Windows, file permissions can be a pain in the
and some modules won't run under Windows. I've had to tweak some modules to make them function properly. Also, XOOPS has a tendency to run slow on IIS even when you optimize it for Xoops, providing your web host will allow the "tweaks".
In short, go with Linux, you will be very glad you did.