Все правильно. Цитата из справки:
>>Syntax
>>MsgBox.Banner (anImageFileName, duration, title)
>> Displays an image file in a modeless window. If duration is non-zero, >>the window will be closed automatically after the given amount of time >>in seconds; with duration 0, the window does not close automatically. >>The image file must be in one of the following singlefile formats: .tif, .im, >>.rs, .xbm, .bmp, and .gif. Returns TRUE if successful.
Но неужели проблема - конвертировать jpg в gif?