Problems adding A form to the sidebar

Hi.

Currently coding a plug in that adds a form to the sidebar. Everything in working perfectly apart from one aspect using PHP (Have very limited Java knowledge).

Currently I’m passing the variables from the form to the same page via $_POST, and even though this works (When the page updates my plug in adds the form information in the way I want), the post I’m on when I use the sidebar form turns to a 404 error, even though the URL is the same.

I assume this is a problem with me not taking account of the Post Id, so I’m looking for a fix for this, either one of two things:

1: way to make the Post not show the 404.
2: A way to only update the sidebar/Form text, without excessive editing of the template, or make the results of the form pop up in a window.