Publisher is pretty lousy at producing websites. It is, as its name suggests, a desktop publishing program and so its layouts are intended for print.
If you have FrontPage you can import the site into a new FrontPage web and then rework the layout to take advantage of dynamic tables. These are tables which have a percentage value of the page size, so a table set at 90% width will always be 90% of the screen resolution it is being viewd on.
Frankly, for the extra work entailed in cleaning up a Publisher produced site I'd give some serious thought to making a new site in FrontPage from scratch. It would probably be just as quick to start afresh than mess around cleaning up all the junk that Publisher produces.
Either way, you should create a new FrontPage web then import all the graphics from your current web into the images folder in the FrontPage web root folder. If you have any downloads on the site, you should create a folder in the web root called downloads to put them in. Follow a simple folder structure like that to keep everything tidy, name all of your files with lower case names - no capital letters or spaces allowed. If you want to use more than one word to name a file, separate the words with an underscore like_this.
FrontPage produces far better output than Publisher ever could, and if you specify a table width to put your page content in, your page will always display at that percentage width on any screen resolution.