In my opinion there are a number of issues:

You need to create syntactically correct mark-up.

Suggest using a method other than Frontpage 5.0.

You are trying to load too many images at start up. Your page took far to long to load and I'm on a fast broadband. Most people would get fed up with waiting and leave before it had loaded.

You need to trap 'previous' and 'next' clicks when there isn't one so as not to produce 404 errors.

To answer your original question, you can disable the buttons and then use JavaScript to enable them once your images have loaded.