According to perlport, seems to be. I don't think windows supports flock until you get into the NT's (2000, XP, etc).

For the time being, you could add the following code to your script to override flock. (NOTE: Only do this for when you run on Windows 98 as the locks are very important with a filesystem that allows concurrent access to files).

BEGIN {
   *CORE::GLOBAL::flock = sub {
      return 1;
   }
}
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Note: Updated code.