No CSS support, and you'll have to drop back to html 4.01, if not html3.2 lol - You'll probably end up writing two seperate versions of the site like I did at one point, or if you're coding in PHP - check $_SERVER['HTTP_USER_AGENT'] for the word "amiga" and customise the output for amiga visitors accordingly
Your DHTML menu probably wont work reliably either, best to have a static list. Its really hard to "meet halfway" using a single version of each page without making it look crap for users with with newer browsers, unless the site's really simple
Sorry to be blunt.