(1) Check your resolution in fireworks is 72 dots/cm2(or whatever that is in inches.
(2) Set you max width in fireworks at 730, that way at 800x 600 res it will still fit on a 14 inch screen. It won't however, fit on anything at 600 x 480 but you have to draw the line somewhere. If you want you can do another page for super low res.
(3) Expand you pags up using tables or % inlayers.
(4) Consider getter a resolution sniffer. in some cases, I've foudn expanding tables up and down to be a problem with layout, so I build three different pages, and set a sniff up based on resolution. The is and extension for this on the web, it might e at MM, I'm not sure.
For the different resolutions, change the iamge size of your fireworks image to match that of each resolution(slightly smaller actually), export it, then set the iamges up in a page spcific to that resolution. Have as your intro page and empty page witht he snifferr that will send users to the right page.