Prompts and Passing information to forms

[imperialized]

OK, I have been trying to figure this out forever. Google has not given me any promising answers either...so I resort to the place that has all the answers, phpfreaks

 

Well, here is my problem.. if you hadn't noticed, I posted prior for help on how to use BBcode.. which I have found my answers, now I have a new problem.

 

When someone clicks on my (url) or (img) button, how do I use a prompt to ask for the URL or the LINK to the image? I know javascript has this option and it is very easy.. Is there a way to pass that variable from a javascript variable into my form?

 

I know this is the code to put data into a form,

window.opener.document.forms['post_news'].elements['news'].value+='$urltext'>

 

I am lost, :-\