ajax plugin

Hi there!
I’m a beginner in WordPress and want to write an Ajax Plugin for the Admin area. Now my head go crazy because many questions on starting up to write this plugin.

First: is in WordPress a hook or so on where i can output html code after the editor when i post a entry?

How i can check, the user is in the admin post side (not the admin feed overview)

Here the short description of the plugin what i want:
After the Editor and on edit the post i want in a div, i want load ajax content.
in this ajax content i have differnt and dynamic count of forms (2 Textfields in one form). The User should can edit delete or add new form.
so i am very pleased if someone can help me or give me tipps for do this plugin