But you were already given a suggestion in this thread:
Try to extract the files in the .zip onto another directory, or another drive entirely. So if you have been trying C:\, try D:\ or even F:\ if you have them. Or the other way around if you have tried a non-main drive first. That should eliminate the password problem. Once you successfully extract the files, cut&paste them into your main PlaneShift folder, clicking Yes to the overwrite prompt. Before you overwrite, make sure that you have no PS processes running - rebooting will do the trick.