Yes as far as I know there is no way to use Ajax to upload files. There is a work around which sets the form's target to a hidden iFrame.
Although I mention Nginx in the blog post the repository contains a component that works with standard Seaside and allows file-upload in the background in an ajax like way.
Nick
_______________________________________________
seaside mailing list
[hidden email]
http://lists.squeakfoundation.org/cgi-bin/mailman/listinfo/seaside