Output content without creating a page or post

Hi there

I’m making a simple plugin where users can make entrys to a database.

My problem is to display forms and stuff generated by my plugin without creating a page or a post, i don’t like to create page templates or shortcodes, links are display in the plugin’s own widget, so when you install it you only have to place the widget in the sidebar.

at the moment, i pass a GET variable to my plugin i.e. action=overview and then add content with add_action(‘the_content’, ‘plugin_overview’)

but now i get the posts on the frontpage too, how can i prevent that or is there an more elegant way to solve this ?

thanks for help