I'm having trouble publishing my story; I can't get it to convert correctly.

This is all I need: italics, bold, centering, horizontal rule.

I've tried ultra simple html created manually. I managed to get this to display correctly in the preview but when I published the story then it centered ALL the story! I tried various things like inserting align left after the centered header but it made no difference.

Then I tried Open Office and saved my file as .sxw. After uploading the preview showed only unreadable codes etc. which looked like .sxw as it would look in a plain text editor.

So, what do I do? I know horizontal rules and centering are possible because I've seen them in published stories.