Thanks a lot for your answers. I've been looking into the Tweetr library and found an example to login and send a Tweet. (this example: http://tweetr.googlecode.com/svn/trunk/examples/flex/example_2.mxml) However, if I click on the "send tweet" button while my username and password are already given, I get a Windows Security Window asking for them again.
Any idea how I can solve this? Kind regards Jef