So Im sitting in Windows waiting on games to download and I was wondering. Can I just download the games in Mac OS and move them to my external hard drive then switch to windows and open them there? Or do I have to download them in Windows?
Possibly depends what you are downloading. If it is just zip/installer(exe) then yes, the OS doing the download does not matter. If it is Steam, then possibly tied to OS (I do not use steam).
Well, as long as the external drive's format is something that Windows can recognize. If it is formatted in hfs (mac) then you won't be able to open the external drive at all from windows (at least not without 3rd party drivers/utilities).