Ok, the answer to your first question is, it depends, I'm afraid. It depends on the site you want to create. From a pure Search Engine and usability angle then Flash graphics with HTML content and navigation (or both of them used as navigation) is a good combination and can be as good as any other normal HTML design out there if designed properly. However, sometimes you want more interactivity, a different interface, etc, etc and making a page entirely in Flash seems more appropriate.
I would say that, sites offering a service should always be HTML unless they can get people to the site through other promotions. Flash sites are usually less serious, so either for the big companies, minisites, strange sites, designers sites, etc.
I would classify your site under "strange site" :razz: and it could definetly benefit from Flash, but then you have to assume that people can't actually find your content... unless you make a HTML version with just the content for the search engines, that forwards real users to your Flash? It's a difficult decision and one that you should make based on how many visitors you get from the search engines themselves and how many of those are to specific pages and not your root / .

Second question: In order to manipulate anything in Flash to a decent degree, you need to convert it to a symbol. If you click on an object, like an image and press F8 then you get to choose between movieclip, button and graphic. In this case you could use movieclip or button. A button would be easier.
so make it a button and then right-click on your new button and choose edit. Select the 'over' frame and press F5 to insert a frame there (which means that your first frame now lasts for two frames). For the button, that means that whatever is in frame 1 will show by default. Frame 2 will show when you mouseoever.

Make a new layer, select the over frame for that layer and press F6 to make a new keyframe in that layer. If you now go down to the 'properties' panel (at the bottom) or if you don't have it, go to windows > properties and always have it on screen as it's extremely useful. Select your sound from the drop down list and leave 'Effect' as event. If you don't have any sounds in the list then go to File > Import and import one!

If you then press CTRL and ENTER at the same time, you'll get a preview of the movie... Just bear in mind that if you mouseoever the button several times then you get the sound played for each time, overlapping any others. There are ways to prevent that, but they are more complicated, so if your sound is short, this first method should be ok..!

And all of that without any actions? Not bad, eh?