Recently I changed my menu to a css based menu which allows me to use alt tags. I ranked 3rd in MSN before changing my menu and now have dropped to 79. MSN's States Loading pages with irrelevant words in an attempt to increase a page's keyword density. This includes stuffing ALT tags that users are unlikely to view. Do you think that adding a just description to the alt tags in my css based menu is behind the drop?
What you have done is messed up the balance by changing the menu although there is probably nothing wrong with it or your alt tags, if you want your ranking back you can put the page back exactly as it was if you have a back up then once MSN gets around to your site again you should rank exactly where you did before, or you could just make your site better by getting more inbound links... Post up your menu
Though spiders can crawl the script, I don't think this is the problem of the change to css. MSN places more weight on page optimization than google, but page optimization is an issue of page content. My suggestion is just working on SEO and wait a few days. BTW, could you post the scripts for your menu?