In Ash's case, either he/she is going over the network (logged in either as the user or the administrator) which means that Windows is still doing all the access (and therefore using Windows security), or if physically mounted, he/she has the special group Everybody granted with full rights on the volume.
I was worried about this on a 1TB portable drive I got for my birthday/Christmas. But when I checked security, the entire drive had been marked to give Everybody full access. So when I move the drive to another computer, I will still have full access to all the files, and can add more files that I know I will be able to access on other machines.
Dealing with getting the data off other hard drives from previous machines can be a pain. You have to grant ownership to the directory (if done through properties, you have to completely get out of the properties dialog to continue making the further changes you need to make, which usually entails setting yourself up with full rights (getting ownership does NOT automatically grant you those right!), and applying them to all the subdirectories that may reside under that directory.
Is the password entered upon user account login, or each time the file is accessed? – Zombies – 2012-12-30T14:42:06.237
@Zombies: It's entered on login. From your account, encrypted files work just like regular files. – SLaks – 2012-12-30T14:43:50.403
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As Ash noted in his answer, it's trivial to mount the volume on a Linux OS and have the ACLs completely ignored. They're not enforced if the OS doesn't understand them. Conversely, *nix permissions don't work on Windows either. See http://security.stackexchange.com/questions/26041/what-mechanism-enforces-user-permissions-in-unix-linux
– Polynomial – 2012-12-30T20:10:02.3532@Polynomial: That's what I said. – SLaks – 2012-12-30T20:13:09.387
@SLaks You said that the OS enforces it, yes; I was just expanding on that. Figured it was worth providing a link to the Sec.SE question. – Polynomial – 2012-12-30T20:38:56.660