I would suggest using .gifs for all your image files save those in a "gallery page" where framed thumbnails are linked to .bmps or jpegs of large images that ope in a new frame or window.
Although most folks seem to have HS Internet Access - they are a significant number of potential customers on DSL and Dial-Up.
The best sites IMHO are those one can speed through, drilling down to the information required quickly and simply. "Begin with the end in mind," is a good thought to hold when designing a site.
So many folks get entangled in the FLASH that the resulting site detracts from its raison d'etre.
KISS is another principle one might embrace in the design phase.
The best designs are completed on paper and de-bugged on paper. Only then should one decide upon the tool(s), templates, software needed to create the pages to put up on the web.
Unfortunately, it is easier to get something up on the web by writing it in a software "package" replete with its own tools and templates that tend to define the sructure for you.
I admit to having taken the later route for my web adventures to date. But, were I creating a commercial venture I would design my site irrespective of the tools at hand and commission someone else to craft the final product / code.