Your question is too vague. What editor program are you using? As an example: if you use tinymce, you can retrieve and store the formatting by calling:
tinyMCE.get( theTextAreaInput.id ).getContent();
This will return a string similar to:
<p><b>This is bolded,</b> but this is not</p>
EDIT: nicEdit works exactly the same way:
[nicInstance].getContent()
http://wiki.nicedit.com/w/page/521/Javascript%20API
And FYI: nicEdit recommends you switch to tinyMCE.
Nicedit is no longer under active development, you might want to try CKEditor or TinyMCE instead.