Ajax uploader

http://blog.joshuaeichorn.com/archives/2006/03/14/php-ajax-file-upload-progress-meter-updates/
"... The basic way the code works is we take a form containing a file upload and submit it using a hidden iframe as a target. Doing this lets the upload happen in the background. Then we poll the server on a regular basis (say a 2 second interval) asking it for update status.
..."

Digest:
1. need a hidden iframe
2. form submit action target the hidden iframe
3. poll server to update the status

[Q] how to add forms to Asp.Net as it comprise only one form?