VAST 8.0.3 does ship with Seaside 3.0.2, but does not support continuations, so there are a few methods in Seaside that won't work. The most prominent one being call:/answer: (unfortunately, call: seems to work initially, but then answer: will fail miserably).
So you need to find a way of not using Continuations (which, btw. is a good idea anyways for most Web applications you want to write these days with all the AJAX bells and whistles).
As a starting point, you can take a look at this blog post: http://joachimtuchel.wordpress.com/2010 ... wonanswer/
Please note: The lack of Continuations also means that you cannot use WATask for your control flow. Again, this sounds much worse than it is. You'll probably end up with a master component that swaps its #children based on your application state, just like you'd implement it in a normal GUI program.