form_remote_tag does not support the input type=file.  This is due to
javascript security limitations.  I created a plugin that modifies
form_remote_tag so that if you pass it the option: :html => 
{:multipart =>  true}, it will submit via an iframe, allowing you to
upload files.  It works nicely with file_column :).  Currently, it
only works with RJS templates (no :update option), and I only
implemented the :loading callback.  Patches are welcome to flesh out
the functionality, but I'm sharing it now because it's still quite
useful.

http://svn.kylemaxwell.com/form_remote_upload/trunk

Patches, bugs, etc via email or at dev.kylemaxwell.com

--
Kyle Maxwell
Chief Technologist
E Factor Media // FN Interactive
kyle@[...].com
1-866-263-3261