I actually did try all of that already before posting. Interestingly enough, it "works" in the sense that it's able to be open and modified, but it won't allow saving. I mean, you can click save, and it asks you to save when you exit, etc, but no matter how many times I save, it doesn't actually save, and the changes aren't kept.
I've actually tried looking for a solution online to the saving issue, but most of the issues happen from people being unable to save "in game", not the editor.
This doesn't seem to work either. I actually do own RPG Maker XP, I have for a long time now actually. I tried a 3rd-party .rxdata editor, and while it actually opens up the data to be modified, it crashes within 30 seconds, which isn't enough time to actually make any changes.
Very weird.