This is exactly why a professional should be hired to build a business website.
iWeb, like any other build your own website tool, writes the code for you. Different browsers interpret the code and fonts differently. There is a lot of bad code written by these programs. iWeb is designed to write code for webkit based browsers(Safari and Chrome). It would take a professional web developer to write code that works well across browsers.
----------
The main problem with the top navigation is you are trying to use a font that the pc doesn't have so it is substituting another font.