I finally got an external harddrive (yay!) but now I need to put stuff on it. The goal is to get all my pictures and music off of 3 different computers into one place. 2 of the computers are PC's, 1 is a mac. I have the external plugged into the mac right now, time machine (which I've never used) came up, and now its telling me to reformat the external hard drive. Will this make it so I can't use it on the PCs? I'm so confused!