Ive looked at your page and it is full of images (none of them with ALT tags specified, hence the reason the validator has complained so much), my guess is youve used fireworks or dreamweaver to create you page which has created the images without you realising.
Simply put, ALT tags are the little yellow boxes that pop up when you roll your mouse over an image to provide a little description of whet the image is or does.
For instance, if you add ALT="Visit the site map" inside the image tag you posted,
Quote:
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..19" border="0" src="imgs/sitemap.gif" ALT="Visit the site map"></A><BR>
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, then when you pt your mouse over the sitemap image in you menu a box will appear.
Whilst these arent strictly necessary they are used by narrators for people with poor eyesight so should not really be overlooked. Google for ALT tags for a more in depth explanation.