Javascript doesn't have access to your files, so it's not really anything with the plugin. You can, however, upload to a hidden iframe. It's very hackish, though.
Hey Daan-
There is a plugin called respond_to_parent that will allow you to return rjs to the iframe and have it eval'ed in the parent window.
http://sean.treadway.info/svn/plugins/responds_to_parent/README
-Ezra
does anybody know how to install the dang thing?
http://weblog.techno-weenie.net/articles/acts_as_attachment
I got as far as this:
rake test_plugins PLUGIN=acts_as_attachement (in /x/home/foobar/docs/thefoobar.com/thefoobar) /usr/bin/ruby18 -Ilib:test "/usr/lib/ruby/gems/1.8/gems/rake-0.7.1/lib/rake/rake_test_loader.rb"
real helpful instructions there buddy 
I manually create the tables, but still no luck. http://weblog.techno-weenie.net/articles/acts_as_attachment
rake test_plugins PLUGIN=acts_as_attachement (in /x/home/foobar/docs/thefoobar.com/thefoobar) /usr/bin/ruby18 -Ilib:test "/usr/lib/ruby/gems/1.8/gems/rake-0.7.1/lib/rake/rake_test_loader.rb"
real helpful stack trace there buddy.
