refurbish small website to comply with div. Webrowser ond MacOSX and Windows (2000/XP Home & Pro)

Look at our website : [login to view URL], which was produced through iWeb 2.0 by me. It works well at my computer, when direct browsed. If browesed via Host, bugs occure (Safari & Internet explorer; Firfox works perfect) on MacOSX (10.4.8) and Windows XP. I look for an overhaul, to get it bugfree for Firefox, Safari, Moszilla IE 5.2 to latest Version on MacOS (Minimum 10.2), Windows XP, 2000 (Home & Pro). HTML code is available (appr. 7.2 Megabyte) also all pictures. No new design or any new features are needed so far, so a plain job.