well, i think you are asking to have some text ( help text ) entered when the user _first_ gets the box to popup.

ie: when there is no files yet added.

so, if you look @ the filemanager.tpl file you will see a smarty {if...} statement for various conditions with {else}

you will notice specificically {elseif !$files} ( basically if NOT any files )

that is the case when there are not yet any files and probably where you would put your 'help text'

so maybe just before {$lang.NO_FILES} line, you could put for example:

HTML
<div class="fm-help">
Hi there earthling. This is some very useful help text that<br />
will guide you thru the maze of uploading a picture<br />
bla bla bla and visit sirdude.com, because he likes pink bunnies!
</div>

you can try that and you will see the result. that should be a starting point and you can ask questions to further refine it smile

note: i put class="fm-help", so you can style that in your Extra CSS portion of your style(s) to maybe give it a different css look/feel from other text. make it more 'helpy' wink