For maximum reach use gifs.
and there are a lot of people out there using IE 3.0 & Netscape 4 who can't see fancy websites. Stick to HTML 4.0 if you can.
check the site live from another machine/modem.
It is amazing what you can miss - trust me I have been there and made these miatakes.
Post the URL when you are ready and you will get a few useful comments.