Most simple way to integrate a html/jquery block into the system? i want to build a form with jquery and html without using drupal forms api (looks too complicated for me to put effort on that). How can i do this? 
How do i have to use a node and how would that be visible? 
Does anyone know a tutorial for this?

I would appreciate any kinds of hints...
Surely you could just build the HTML form as you normally would, and set the Filter Format to Full HTML (if you're using the WYSIWYG).  Seems an odd way of doing things though to be honest!

You could also take a look at the Webform module.  That'll allow you to store form submissions easily as well!  Or Form Builder, but I've never used it before and it doesn't appear to have a 1.0 release.

On another note, the form API in Drupal is not only REALLY powerful, but actually easier than it looks!  It's definitely worth taking time to learn, as you'll find yourself coming back to it again and again!