I use Dreamweaver MX for my code validation, as well as the free code validators at the WC3 site.
Also, about the preloading thing, some browsers have issues with it, however the latest do not.
The only thing I can think of is that the errors migh have been caused from bad links to the images themselves.
For example, if your images are in a separate "Images" folder, then yor preloader code should look like this:
<html>
<head>
<script>
preloadimages("images/bigsmile.JPG","images/bigsmile1.JPG")
</script>
</head>
Cool?
Israel "Izzy" Long
Motion and Title Design for Broadcast-Film-DS
izzylong.com