CODEMAN38  (Sorry for spamming this thread... but just trying to help anyone else with the same issues.)

Here's a very kludgy workaround to select a video for a new script under Leopard when the script settings dialog disappears:

Press Shift+Tab twice. (This moves the focus to the (now invisible) button to select the movie file.)

Press Space.

Select a movie and click OK.

Press Tab. (This moves the focus to the OK button.)

Press Space.

Press Cmd+S to save.

Press Cmd+W to close.

Re-open the Miyu file from wherever you saved it, and the window should appear with the correct video in it.

Hope this helps hold everyone over until RC5 is released...  
(Version 1.0rc4)

CODEMAN38  Ignore my above comment; I spoke too soon. For some reason, the dialog box *did* show up for me once in 10.5.1, while it never showed up in 10.5.0. And now it's not showing up again. Definitely a bug in Miyu.  
(Version 1.0rc4)

CODEMAN38  Actually, never mind - hadn't tested it since upgrading to OS X 10.5.1 yesterday, and the OS upgrade seems to have fixed this annoyance. So anyone else having the same issue, update to 10.5.1.  
(Version 1.0rc4)

CODEMAN38  Unfortunately, Miyu 1.0 RC4 is incompatible with OS X Leopard; the dialog box where one is supposed to select the source video just vanishes, making it impossible to continue.

Hoping this gets fixed as soon as possible... I *really* like this app; it's the best thing I've seen on Mac for generating SSA formatted subtitles.  
(Version 1.0rc4)