That's exactly right. When I build websites I have three computers with different size screens and several browsers. I check them all to make sure nothing bad happens like scrolling sideways. But it will look different on several. The CSS scripts help minimize these diferances.
My comment on picture size was the height, not width. IMO the height takes up to much room and you immediately have to scroll down. In the long run the basic pages in the site will have to look similar to the forum. As it stands now when you go from the website home page to the forum it looks as though you went to a different website.