Here is what I got from Ruud. Basically, it has nothing to do with the OS, but rather to do with IE:
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EnumIPInfo depends on IPHLPAPI.DLL, and that is only installed with IE 5.01 or higher. Previous builds (inc b2) had a hard link to this DLL, but the latest build silently fails the call and sets @error instead.
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Uhm, so who was it that said IE was not part of the OS?