Is it possible to make a program that open a page (as if a bookmark file were opened by IE), and based on its content generate a feedback, that should be fedback in a textbox on said page by pressing a button on said page?
I need this program to execute on a set time schedule to feed some data to a web server based on time dependent web page data.
Yes, that is possible. It is generally called screen scraping. You basically retrieve the web page in question via a HTTP request, parse/analyze the page you got, then send back the data that should go into the textbox (again a HTTP request).
There are libraries to do that. Here is an article describing an example in Perl: http://www.perl.com/pub/a/2003/01/22/mechanize.html