If your drive already has data on it, and you're attempting to use Disk Utility to repartition it, yes, everything will get erased. If it's blank and you partition it now, and want to format one partition later FAT32 on a Windows box, AFAIK, only the partition that you want to format will be erased.. same as it would on a Mac. Is there a 3rd option that you're referring to that I'm missing? It's Friday and I cannot concentrate very well..