Create user on content creation In a "course" content type, I have an "instructor name" field, which points to a registered user.

When the "course" content is saved, I need to check if there are any registered users with the name in the "instructor name" field. If there is, I'd like to relate the created content with his id. If not, I'd like to create a new user (a dummy user maybe)  and relate the content with that user.

Is this possible without php coding, just using modules? And if it is, how? I am a new drupal user with .net background and have no knowledge of php.
Yes, you can do it with Rules module.

Basically, after enabling the Rules &amp; Rules_UI module, you create a new Rule acted on a node is created, add an action of creating a new user entity. You need to spend a bit of time to specify the condition to suit your need. 

Some screenshot of flow attached for you.