I'm currently using GameEditor 1.4.1b (though it did the same in 1.4.0) on Windows XP SP3.
When I create a new actor, and assign it an animation, as soon as I try to add a second animation, the dialog box opens, but when I click the box to select the file, the program just becomes unresponsive.
On the download page, Windows XP was part of the list of supported Windows platforms, so it should not be a matter of incompatibility.
Thanks for any responses!