Office 2003 has its own GUI theme and mose accepted that no problems, so creating your own shouldn't be frowned upon.
So long as the app does not launch itself into full screen mode and its window can do the usual, min, max, resize & move then I can't see many people freaking out because it doesn't have the usual Win9X / XP look to it (again, office 2003 doesn't either).
Recently I've been using Office 2003 style GUI components in my Delphi apps and no one has said "eeek, can you make it look more normal", infact they like it.
In the end though its how your app functions. User friendlyness is more important than a fancy GUI.
So long as the app does not launch itself into full screen mode and its window can do the usual, min, max, resize & move then I can't see many people freaking out because it doesn't have the usual Win9X / XP look to it (again, office 2003 doesn't either).
Recently I've been using Office 2003 style GUI components in my Delphi apps and no one has said "eeek, can you make it look more normal", infact they like it.
In the end though its how your app functions. User friendlyness is more important than a fancy GUI.